home Adviсe Factors influencing test results. When is a blood test ordered? Factors influencing laboratory results

Factors influencing test results. When is a blood test ordered? Factors influencing laboratory results

In addition, during registration, medical products and equipment that are measuring instruments are included in the state register of measuring instruments. A verification scheme is developed and approved for it. It is this equipment that must be regularly subjected to state metrological control in the future. It should be noted that medical products that are not included in the register of measuring instruments are not subject to metrological control and supervision (!). This information is presented in more detail in the letter of the Ministry of Health of the Russian Federation dated 29/3 - 2007 No. 01I-231/07: “On State metrological control and supervision of medical products.”

Research Quality Assurance at the level of an individual institution healthcare consists of the development and implementation by staff of clinical departments of measures to prevent a negative impact on the quality of results laboratory research factors of the preanalytical and postanalytical stages. The factors of the preanalytical stage include the impact of diagnostic and treatment procedures on the state of the internal environment of the examined patients; as well as violations of the rules for taking, labeling, primary processing, storage conditions and transportation to the laboratory of samples of biomaterials taken from patients. Factors at the post-analytical stage include inadequate interpretation of the study results.

Quality assurance at the level of clinical diagnostic laboratory is to develop and implement measures to prevent the negative influence of factors that can interfere with obtaining a reliable result of a laboratory test, both at the preanalytical stage and at the analytical and postanalytical stages. At the analytical stage, prevention of violations of the rules for conducting the analytical procedure, errors in calibrating the method and setting up the measuring device must be organized, and the purchase and use of reagents and other consumables that are not approved for use in the Russian Federation must be excluded. The post-analytical stage includes an assessment of the credibility and reliability of the research results obtained, and their preliminary interpretation.

3.2. Factors influencing the quality of laboratory tests. Classification of factors

One of the most important requirements for laboratory research is an objective reflection of the state of the internal environment of the body. Fulfilling this requirement is very difficult, since the patient’s condition is constantly changing. It is for this reason that it is generally accepted to take biological material at the same time in the morning before taking medications and undergoing instrumental examination or treatment. In addition, the procedure for “collecting” samples should be low-traumatic so as not to cause stress and not cause a change in the concentration of the components under study. Samples must retain their composition before the start of the study, be correctly analyzed, not mixed up and, finally, correctly interpreted.

For the convenience of analyzing processes and finding bottlenecks in laboratory research, it is customary to distinguish three stages - preanalytical, analytical and postanalytical (Fig. 15).

Each specific health care facility develops its own rules for handling biological material, schemes for its delivery, storage, analysis procedures, and, accordingly, the reasons for errors in different medical institutions will vary somewhat. It is safe to say that the most effective measures will be those that are aimed at eliminating frequently occurring errors. Therefore, to improve the quality of research, it is necessary to constantly actively identify problem areas and eliminate them. It is much easier to carry out this work if all errors and malfunctions are recorded.

The occurrence of errors at different stages of the laboratory process can be analyzed using the example of one of the laboratories in Thailand, in which their type and frequency were recorded for 6 months. This laboratory was certified according to the ISO 9002:1994 standard, one of the requirements of which is a clear and complete recording of errors that occur, which made it possible to objectively assess their number. The total number of studies during the observation period was: 941902. At the same time, 1,240 errors were registered, which is 0.13% of all studies conducted. When analyzing the causes of errors, it turned out that only 12 errors (1.15%) were associated with a failure in the computer system, while all the rest were caused by the actions of personnel. Sources of errors are presented in more detail in Table 2.

As follows from the data presented, errors occur at all stages of the study, however, much more often they occur not during the actual laboratory analysis (analytical stage), but at the preanalytical stage (in the given example - 84.52%) and, much less often, at post-analytical (11.13%) stages.

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table 2

Number of errors at different stages of laboratory research

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Rice. 16. Number of errors at different stages of laboratory research

Table 3

Frequency of occurrence of different types of errors at the preanalytical stage

The reasons for the errors that arose at the pre-laboratory stage in the laboratory diagnostics department of the IDC were shown earlier in Figure 6.

Thus, according to numerous observations, the percentage of errors in laboratory medicine is 55-95% associated with the preanalytical stage, primarily with its extra-laboratory stage. The preanalytical stage is a set of activities (processes and actions) performed from the moment a doctor prescribes laboratory tests to the start of an analytical measurement (for example, loading samples into a biochemical or hematological analyzer, etc.) (Fig. 17).

We list the factors influencing the results of laboratory tests that need to be known, taken into account and standardized.

1. Biological factors:

1.1. Constant and not changing

Race, gender, age

1.2. Changeable and subject to influences

Diet, physical activity, lifestyle, medication, body weight, smoking, drinking, etc.

The presence of lipemia and icterus in the blood.

Decreased erythrocyte stability (hemolysis).

Presence of endogenous antibodies (cold aglutinins, cryoglobulins, heterophilic antibodies, autoantibodies).

Time of material collection (circadian rhythms, phases menstrual cycle, last meal...).

Pharmacotherapy administered to the patient, including the administration of infusion solutions (blood dilution).

Body position when taking material for research.

The difference in the content of analytes in capillary, venous and arterial blood.

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Rice. 17 Operations included in the preanalytical stage of laboratory research

2. Laboratory factors:

2.1. Method and quality of material collection (compliance with the recommendations presented in reference books and manuals).

2.2. Differences in concentrations of analytes determined in plasma and serum.

2.3. Selection of tubes, anticoagulants, stabilizers, separating gels.

2.4. Techniques for identifying samples from individual patients. (Labeling of tubes using barcodes).

2.5. Providing the required amount of material (It is necessary to take approximately 2-4 times more material than is necessary to perform this analysis).

2.6. The influence of time, temperature and mechanical influences during sample transportation from the sampling site to the laboratory.

3.3. Sources of error in the preanalytical phase outside the laboratory

As already mentioned, errors in the study results may be associated with the patient’s physical and emotional state, body position, and the effects of medications. Physiological factors that determine the level of indicators in healthy individuals include race, sex, age, body type, physiological activity cycle, time of last meal and diet composition. Environmental factors include the influence of the social environment, climate, altitude, geomagnetic influences, soil and water composition in the habitat area.

Diagnostic and therapeutic measures may influence the results obtained. If the influence of these factors is not taken into account, the meaning of laboratory information may be distorted.

Venipuncture- has a certain psychological and physical effect on a person with hypersensitivity to pain or with mental lability and thereby become stress for the subject, causing an increased level of adrenaline in the blood.

Administration of urinary catheter- can also increase the activity of acid phosphatase in the blood, which sometimes leads to an unjustified assumption of a prostate tumor.

It is necessary to take into account the influence of various therapeutic measures on laboratory parameters, especially since these effects can be quite significant.

physical (including up to electric current high voltage);

chemicals (medicines);

biological (administration of vaccines, serums);

For example, treatment with ATS stimulates the secretion of hormones from the adrenal cortex, which leads to changes in nitrogen metabolism, increased glucose levels due to gluconeogenesis, increased lipolysis and increased NEFA content in the blood.

Isoniazid, methyldopa, sulfanilamide - increase the content of bilirubin in the blood serum.

Acetylsalicylic acid in the treatment of rheumatism leads to an increase in ALT activity.

The pharmacological effect of drugs on laboratory parameters may depend on the dose and duration of use of the drugs, and on the patient’s individual sensitivity to them.

The effect of a drug or its metabolites is determined during laboratory testing, i.e. it can be reproduced by adding drugs to a sample of blood serum or other biological fluid.

Biological and other factors

Among biological factors, one can distinguish a category of those that should be taken into account, but which cannot be changed. It's easiest

permanent factors- racial, national, i.e. ultimately genetically determined.

factors that have a long-term physiological effect- gender, age, body type, habitual physical activity, cycle and nature of nutrition associated with national and local traditions, customs, conditions.

environmental factors- geographical, climatic, time of year, features food products in the environment of habitual habitat, determined by the composition of soil, water, as well as social factors.

genetic factors are able to change laboratory readings of the concentration of free cholesterol, HDL, LDL depends to a greater extent on genetic factors than on environmental factors.

Depending on age, people are clearly divided according to the nature of laboratory indicators into four groups:

Newborns

Adults

Aged people

Physiological short-term variations may be regular or random.

Regular- observed over a 24-hour period (so-called circadian rhythms). Daily rhythms of fluctuations in the content of electrolytes, steroids, phosphates and water in urine are known. Diurnal fluctuations in plasma cortisol levels are diagnostically important. To limit the influence of diurnal variation on test results, samples should be taken at the same time of day (preferably early in the morning and on an empty stomach).

Physical activity causes shifts in enzyme activity values, which must be taken into account when examining outpatients.

Plasma protein concentration varies depending on body position (it is lower in the supine position than in the standing position). With different body positions, the content of potassium, calcium, albumin, AST, acids and alkalis, phosphates, phosphorus and cholesterol also changes.

Laboratory results are subject to biological and analytical variations. If analytical variation depends on the test conditions, then the magnitude of biological variation depends on a whole complex of factors. The general biological variation of the studied parameters is due to intra-individual variation observed in the same person as a result of the influence of biological rhythms ( different time day, year), and interindividual variation caused by both endogenous and exogenous factors, the main of which are presented in Fig.

Factors of biological variation (physiological factors, environmental factors, sampling conditions, toxic and therapeutic factors) can influence the results of laboratory tests. Some of them can cause real deviations of laboratory results from reference values without connection with the pathological process [Menshikov V.V., 1995]. Such factors include the following.

■ Physiological patterns (the influence of race, gender, age, body type, nature and volume of habitual activity, nutrition).

■ Environmental influence (climate, geomagnetic factors, time of year and day, composition of water and soil in the habitat, social and living environment).

Rice. Sequence of evaluation of laboratory test results

■ Exposure to occupational and household toxic substances [alcohol, nicotine, drugs) and iatrogenic influences (diagnostic and therapeutic procedures, drugs).

■ Conditions for taking a sample (food intake, physical activity, body position, stress during sample taking, etc.).

■ Method of collecting blood (method of collection, means and utensils, preservatives, etc.).

■ Incorrect (timing) collection of material.

■ Conditions (temperature, shaking, light influence) and time of transportation of biomaterial for research in the laboratory.

Rice. Factors influencing biological variation [Garanina E.N., 1997].

Let's consider the influence of the most important factors on the results of laboratory tests.

Eating. Diet, composition of food intake, breaks in its intake have a significant impact on a number of laboratory test indicators. After 48 hours of fasting, the concentration of bilirubin in the blood may increase. Fasting for 72 hours reduces the concentration of glucose in the blood in healthy people to 2.5 mmol/l (45 mg%), increases

the concentration of triglycerides (TG), free fatty acids without significant changes in the concentration of cholesterol (CS).

Eating fatty foods can increase the concentration of potassium, TG and alkaline phosphatase. The activity of alkaline phosphatase in such cases may especially increase in people with O- or B-blood group. Physiological changes after eating fatty foods in the form of hyperchylomicronemia can increase the turbidity of the blood serum (plasma) and thereby affect the results of optical density measurements. An increase in the concentration of lipids in the blood serum may occur after the patient has consumed butter, cream or cheese, which will lead to false results and require re-analysis.

Consumption of large amounts of meat, that is, foods high in protein, can increase the concentrations of urea and ammonia in the blood serum, and urate in the urine. Foods with a high ratio of unsaturated to saturated fatty acids can cause a decrease in serum cholesterol concentrations, and foods rich in purines cause an increase in urate concentrations. Bananas, pineapples, tomatoes, avocados are rich in serotonin. When consumed 3 days before urine testing for 5-hydroxyindoleacetic acid, even in healthy person its concentration may be increased. Drinks rich in caffeine increase the concentration of free fatty acids and cause the release of catecholamines from the adrenal glands. Drinking alcohol increases the concentration of lactate, uric acid and TG in the blood.

General rule to exclude the influence of food intake on the results of laboratory tests - blood sampling after a 12-hour fast.

Physical exercise. Physical activity can have both transient and long-term effects on various parameters of homeostasis. Transient changes include first a decrease and then an increase in the concentration of free fatty acids in the blood, an increase in ammonia concentration by 180% and lactate by 300%, an increase in the activity of creatine kinase (CK), aspartate aminotransferase (AST), lactate dehydrogenase (LDH). ) . Physical exercise activates blood coagulation, fibrinolysis and platelet functional activity. Changes in these indicators are associated with activation of metabolism; they usually return to their original (before physical activity) values soon after cessation of physical activity. However, the activity of some enzymes (aldolase, CK, AST, LDH) may remain elevated for 24 hours after 1 hour of intense physical activity. Prolonged physical activity increases the concentration of sex hormones in the blood, including testosterone, andros tendione and luteinizing hormone (LH).

Emotional stress can cause transient leukocytosis, decreased iron concentrations, and changes in blood catecholamine levels. Severe anxiety accompanied by hyperventilation causes an acid-base imbalance (ABS) with increased concentrations of lactate and fatty acids in the blood.

Other factors. Among other factors influencing the results of studies, circadian rhythms of homeostasis, age, gender, pregnancy, geographical location of the area, altitude, ambient temperature, and smoking are important. Smokers may

the concentration of carboxyhemoglobin (HbCO), catecholamines in the blood plasma and cortisol in the blood serum may be increased. Changes in the concentrations of these hormones often lead to a decrease in the number of eosinophils, while the content of neutrophils, monocytes and free fatty acids increases. Smoking leads to an increase in hemoglobin (Hb) concentration, red blood cell count, mean erythrocyte volume (MCV) and a decrease in white blood cell count. In this regard, laboratories are recommended to establish their local reference (normal) values for their population.

In order to reduce the influence of the above factors on test results, before taking blood for testing, it is necessary to abstain from physical activity and drinking alcohol, and changes in diet for 24 hours. The patient should not eat after dinner; he should go to bed the night before at his usual time. time and get up no later than 1 hour before taking blood. It is recommended to draw blood from the patient in the early morning hours after a 12-hour overnight fast (baseline), which allows for maximum standardization of study conditions.

Medicines. Some drugs can have a significant impact on research results. For example, taking acetylsalicylic acid when determining the duration of bleeding according to Duque should be discontinued 7-10 days before the study, otherwise a pathological result may be obtained. If the drug taken by the patient may affect the test result, and if it is impossible to cancel it, the laboratory must be informed about this.

The influence of drugs on the results of laboratory tests can be of two types.

■ Physiological effect in vivo (in the patient’s body) of drugs and their metabolites.

■ Effect in vitro (on chemical reaction, used to determine the indicator) due to chemical and physical properties LS (interference).

The physiological effects of drugs and their metabolites are largely known to practicing physicians. Let us consider the meaning of interference, that is, the intervention of an extraneous factor in the results of the analysis.

Interference can be caused by the presence of both endogenous and exogenous substances in the biomaterial sample. The main endogenous interfering factors include the following.

■ Hemolysis, that is, the destruction of red blood cells with the release of a number of intracellular components (Hb, LDH, potassium, magnesium, etc.) into the liquid part of the blood, which changes the true results of determining the concentration/activity of such blood components as bilirubin, lipase, CK, LDH, potassium, magnesium, etc.

■ Lipemia, which distorts the results of a number of colorimetric and nephelometric research methods (especially when studying phosphorus, total bilirubin, uric acid, total protein, electrolytes).

■ Paraproteinemia, which causes changes in the results of determining phosphates, urea, CK, LDH, and amylase by certain methods.

The most common exogenous interfering factors are drugs or their metabolites. Thus, when determining catecholamines by the fluorimetric method in urine, intense fluorescence can be caused by tetracycline taken by the patient; the propranolol metabolite 4-hydroxypropranolol interferes with the determination of bilirubin by the Jendrassik-Grof and Evelin-Melloy methods.

Identifying drug interference is one of the tasks of a clinical physician. laboratory diagnostics. An important step in solving this problem is contacting the clinician to clarify the nature of the medications the patient is taking.

Body position during blood sampling also affects a number of indicators. Thus, a patient’s change from a lying position to a sitting or standing position leads to hydrostatic penetration of water and filtered substances from the intravascular space into the interstitial space. Substances with a large molecular weight (proteins) and blood cells with substances associated with them do not pass into the tissue, so their concentration in the blood increases (enzymes, total protein, albumin, iron, bilirubin, cholesterol, TG, drugs associated with proteins, calcium). The concentration of Hb, Ht, and the number of leukocytes may increase.

The location and technique of blood collection can also have a significant impact on the results of laboratory tests (for example, applying a tourniquet for a period of time of more than 2 minutes when collecting blood from a vein can lead to hemoconcentration and an increase in the concentration of proteins, coagulation factors, and the content of cellular elements in the blood). The best place to collect blood for testing is the ulnar vein. It should also be noted that venous blood is the best material not only for determining biochemical, hormonal, serological, immunological parameters, but also for general clinical research. This is due to the fact that the currently used hematological analyzers, with the help of which general clinical blood tests are carried out (cell counting, determination of Hb, Ht, etc.), are designed to work with venous blood, and for the most part in the countries where they are produced, they are certified and standardized to work only with venous blood. Calibration and control materials produced by companies are also intended for calibration of hematology analyzers using venous blood. In addition, when collecting blood from a finger, a number of methodological features are possible that are very difficult to standardize (cold, cyanotic, swollen fingers, the need to dilute the test blood, etc.), which leads to significant variations in the results obtained and, as a consequence, to the need for repeated studies to clarify the result. For general clinical examination, it is recommended to take blood from a finger following cases.

■ For burns that occupy a large surface area of the patient’s body.

■ If the patient has very small veins or their limited accessibility.

■ If the patient is severely obese.

■ With an established tendency to venous thrombosis.

■ In newborns.

Arterial puncture for blood sampling is rarely used (mainly to study the gas composition of arterial blood).

The time and conditions of transportation of samples of biological material also play a role important role in ensuring the quality of laboratory research results. When delivering material to the laboratory, it is always necessary to remember the characteristics of some samples. For example, when collecting arterial blood to study the gas composition, the container with blood must be well sealed, immersed in ice water and taken to the laboratory as soon as possible, since glycolysis in red and white blood cells causes a decrease in pH if the sample is left at room temperature for approximately 20 minutes. These requirements must also be observed when studying capillary blood, which is collected into heparinized capillaries. Blood for testing for adrenocorticotropic hormone (ACTH), angiotensin I, II, renin should also be placed on ice immediately after collection and delivered to the laboratory as quickly as possible.

In general, in order to avoid the influence of the time factor on the test results, the material must be delivered to the laboratory as quickly as possible. The earlier the serum is separated from the red blood cells, the less the effect of glycolysis (which means the less effect on the concentration of glucose, phosphorus and the activity of some enzymes). The concentration of bilirubin in the blood decreases under the influence of light (especially bright sunlight). Exposure to light also increases alkaline phosphatase activity. The time factor is also very important in bacteriological studies (some bacteria die at room temperature).

The time for delivery of biomaterial to the laboratory must fit within the intervals presented in the table. If they are observed, it is possible to minimize the negative impact of the time factor on the results of laboratory tests.

Table 1-1. Delivery times for samples to the laboratory

Every clinician should know the specified delivery time standards. If they are violated, repeated sampling is necessary, since it is not possible to exclude the influence of the time factor on deviations in research results.

In addition to all of the above, the magnitude of biological variation depends on the physiological function performed in the body by the analyzed substance. The smallest biological variation is characteristic of substances that are most important for the stability of the composition and volume of extracellular fluids and blood (sodium, chlorides, calcium, magnesium, albumin, total protein, carbon dioxide). Moderate variation is typical for substances involved in anabolic processes (glucose, cholesterol, phosphorus). The greatest biological variation is observed in blood serum components, which are the end products of catabolism (uric acid, urea, creatinine), as well as substances and enzymes released from tissues [LDH, AST, alanine aminotransferase (ALT), etc.].

Find out what factors can distort the results of a blood test. Did you know that even what you dealt with the day before can affect the accuracy of your blood test results? Find out several factors that influence the falsification of a number of blood parameters. So what influences our analyses?

1. Morning snack
Everyone knows that if you donate blood on an empty stomach, you need to come without eating. But is eating, for example, candy or a small snack considered a lack of food? If the research requires empty stomach, it is better to refrain from eating any foods - both large portions and “innocent” snacks. Otherwise, the results obtained may not reflect the actual concentration of many parameters, such as glucose.

2. Alcohol
When preparing for a blood test, it is better to refrain from drinking alcohol 2-3 days before taking the material. Alcohol can affect changes in the concentration in the blood of parameters such as glucose, bilirubin, ammonia, uric acid, lipids and cholesterol, prolactin.

3. Fatty dinner
The last meal of the day before blood sampling should be easily digestible. Otherwise, it may affect the falsification of lipid test results, i.e. studies of the concentration of individual lipid fractions: total cholesterol, LDL cholesterol and HDL, as well as triglycerides.

4. Coffee
Morning coffee (even without sugar) can, for example, cause a false decrease in magnesium and blood glucose levels. To avoid this, before the morning blood draw it is better to replace your morning coffee, for example, with a glass of mineral water. You also need to remember that it is strictly prohibited to consume this drink if you must appear for a scheduled examination on an empty stomach.

5. Time of day
The concentration of some blood parameters may vary depending on the time of day. For example, potassium concentrations are lower in the afternoon than in the morning, and cortisol levels fall during the day and increase at night. When issuing a referral for tests, the doctor will inform you about the time for taking them. If this does not happen, be sure to inquire about it yourself.

6. Large doses of vitamin C
Taking large amounts of vitamin C may affect liver test results, blood glucose levels, or bilirubin levels, for example. Test results can also be affected by large doses of calcium or vitamin D, which affect the concentration of magnesium in the blood.

7. Some medications
Let's give just a few examples. Remember that before the examination you need to tell your doctor about the medications you are taking. Blood clotting time increases after taking, for example, aspirin (and other salicylates), they reduce blood glucose levels and affect hormone concentrations thyroid gland. Pain medications affect blood ammonia and glucose levels, as well as liver function tests. Diuretics lower potassium and glucose levels in the blood. Antibiotics may, in turn, interfere with enzyme and lipid profile tests. Cold medications can change the concentration of uric acid, and drugs that have an anti-inflammatory effect can change the results of liver tests.

8. Oral contraceptives
If you are taking oral contraceptives, it is worth informing your doctor before going for a blood test. Of such kind contraception are able to influence the concentration of prolactin, a hormone responsible for the regularity of the menstrual cycle, lactation and pregnancy maintenance. They also affect the concentration of magnesium and iodine.

9. Smoking
U heavy smokers determined increased level leukocytes (white blood cells). They also have increased lipoproteins and the activity of certain enzymes. Smoking a cigarette an hour before the scheduled delivery of biomaterial increases the level of adrenaline, cortisol, aldosterone and free fatty acids. Therefore, all smokers should inform the specialists who receive and analyze their blood about their addiction to tobacco.

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Another example: in menstruating women, blood loss may be accompanied by a decrease in hemoglobin and hematocrit levels. Thus, reference ranges for these indicators must be assessed taking into account both the age and gender of the subject.
Other factors influencing research results

Typically, laboratories, along with the test results, also report the reference range of results for a given subject, taking into account his age and gender. After this, the doctor will need to evaluate the results obtained in accordance with the individual data about the patient, including the medications and herbal preparations he receives. In addition, many other factors may affect the results of the study: coffee consumption, smoking, alcohol or vitamin C intake; diet (vegetarian or meat); stress or anxiety; pregnancy. Some results may even be affected by the position of the subject’s body at the time of the study, as well as the presence of physical activity before the test. For example, standing up from a lying position may increase albumin and calcium levels in the blood.

A number of rarely taken into account factors can also influence the results of the study, for example, the profession of the subject, altitude above sea level, distance from the ocean. In addition, the results of some studies can be affected by physical activity (in particular, during exercise, the levels of creatine phosphokinase - CPK, aspartic aminotransferase - AST, lactate dehydrogenase - LDH increase). In addition, during prolonged intense physical activity (for example, marathon runners and weightlifters), levels of testosterone, luteinizing hormone (LH), and platelets may increase.

All these examples show that for the correct assessment of the results of laboratory (as well as outpatient - carried out at home) tests, it is important to obtain blood and urine samples under standardized conditions. In preparation for the study, the subject is required to follow the doctor’s instructions, for example, to come to donate blood for the study in the morning and on an empty stomach. Following these guidelines will allow the analysis to be carried out as close as possible to general requirements, and thereby bring the study results as close as possible to the reference ones for this group of patients.

When “norms” are not considered

In some studies, for example, when determining cholesterol levels, in the vast majority of cases, instead of determining reference ranges, it is enough to only assess whether the result exceeds a certain threshold value, the so-called “red flag”. IN scientific research it has been shown that when cholesterol levels rise to 200 milligrams per deciliter, the risk of heart damage increases enough to require treatment; in this case, the relationship between the research results and the ranges of statistically “normal” values no longer plays a role.
In addition, reference ranges are not considered in a number of other situations. For example, determination of the blood level of a particular drug in an unconscious patient is carried out to assess the intended effect of that drug, and not the relationship of the concentration to the reference range.

In addition, a medical assessment is required when there is a marked change in indicators of medical significance, even if they do not fall outside the reference range.

How are study results outside the reference range assessed?

According to probability statistics, every twentieth (or 1 in 20, or 5%) study result may fall outside the true reference range; therefore, the result of an individual study cannot be considered statistically significant. Typically, study results are only slightly outside the reference range. However, it should be remembered that in a healthy person, if the same study is repeated 20 times, with a high probability one of the results of this study will be outside the reference range, despite the fact that the subject does not have any health problems.

Of course, sometimes results outside the reference range indicate disease. The first thing a doctor should do to check this is to repeat the test. It is possible that the test result outside the reference range was due to one of the reasons mentioned above, or the rules for processing the test sample were violated (the blood sample was not frozen, or the serum was not separated from the red blood cells, or the sample was kept warm).

Typically, laboratories present the results of the study taking into account the age and gender of the subject, and the doctor, when assessing them, also takes into account other factors, in particular, the diet and level of physical activity of the subject, as well as the amount he receives. drug therapy. If any factors may affect the test results, be sure to tell your doctor about them.

Why is this document not providing specific reference ranges?

Although we discuss issues related to reference ranges in some detail, these ranges themselves are almost not given in our document.

There are several reasons for this:

Common Misconceptions

There are two common misconceptions regarding research results and reference ranges:

Opinion: “A deviation of the test results from the norm means the presence of a disease.”

Truth: Study results outside the reference range do not always mean the presence of a disease - it is only a sign for the doctor about the need additional examination. Sometimes deviations in test results from the norm occur in completely healthy people - but it is better to leave the right to decide on this to the doctor.

It is possible that the test result will be among the 5% of normal results that are outside the statistically determined reference range. In addition, it should be remembered that the results of the study can be influenced by a large number of factors that do not indicate the presence of the disease: for example, high level Blood glucose levels may not be due to diabetes, but to high sugar in the diet. Lipid (fat) levels may be high if the person being examined has eaten shortly before receiving blood for testing. Liver enzyme levels may rise temporarily after drinking alcohol, and these increases do not necessarily indicate cirrhosis. New drugs are constantly appearing on the market, and laboratories do not always have time to check whether taking these drugs affects the results of studies. It is not uncommon for many of these medications to interfere with the results of some studies without the change being medically significant. Most likely, if deviations from the reference range are detected, the doctor will decide to repeat the study. Sometimes altered results, especially those near the edge of the reference range, normalize on their own. In addition, the doctor will try to find an explanation for the identified changes in results; perhaps it would be one of the explanations given above. The key question will be: how far does the result deviate from the reference range?

If the results of the examination reveal the disease, the doctor will be able to clarify its severity. However, very rarely is one study sufficient to answer these questions.

Opinion:“If the test results are normal, there is no disease.”

True: Of course, it is nice to get such results, but they do not at all guarantee that everything is in order. The results of studies in healthy and sick people often overlap, so when analyzing the results there is always a small chance of missing an existing disease. Just as some healthy people have laboratory results outside the reference range, some sick people have laboratory results within this range. If you are trying to comply healthy image life, such results show that you are on the right path. However, if your behavior is associated with risk factors, such as drug and alcohol abuse, dietary errors, these results will only be good for a while and should not be expected to last long. Good research results are not an indulgence in a bad lifestyle.

If abnormalities in laboratory parameters were previously detected in you, the appearance of normal test results certainly indicates a favorable change in the course of the disease. However, in many cases, the doctor still decides to repeat the studies after a few months to ensure that the favorable changes are maintained and to prove the presence of a corresponding trend.

General blood analysis

Hemoglobin (Hb) is a blood pigment and the main respiratory protein in the blood that transports oxygen to organs and tissues.

Hemoglobin is normal:

In men - 130–160 g/l;

For women - 120–140 g/l.

A decrease in Hb concentration in the blood indicates anemia of one degree or another (a drop in its concentration to 40 g/l requires urgent measures, and the minimum Hb content at which a person’s life continues is 10 g/l).

Normal red blood cells:

In men: from 4.5 1012 to 5.3 1012 /l (or 4.5–5.3 T/l);

In women: from 3.8 1012 to 5.1 1012 /l (or 3.8–5.1 T/l).

A decrease in the number of red blood cells below 3.5 G/l characterizes the development of anemia syndrome. The presence of aniso- and poikilocytosis indicates destructive disorders in erythrocytes. In healthy people, the diameters of erythrocytes range from 5 to 9 microns, with an average of 7.2 microns. The erythrocytometric curve (Price-Jones curve) is a graph of the distribution of erythrocytes by their diameter, where the values of erythrocyte diameters (μm) are plotted along the abscissa axis, and the percentages of erythrocytes of the corresponding size are plotted along the ordinate axis.

Anisochromia - a change in the color of red blood cells - depends on the hemoglobin content in them. Polychromasia - the simultaneous perception of acidic and basic colors by red blood cells - indicates enhanced blood regeneration. A change in the properties of red blood cells to withstand various destructive influences - osmotic, thermal, mechanical - has a certain diagnostic significance.

Reticulocytes are young forms of erythrocytes that retain granularity (remnants of the basophilic substance of the cytoplasm). In healthy people, the normal level is 0.5–1% of reticulocytes.

The color index (CI) depends on the volume of red blood cells and the degree of their saturation with hemoglobin. Normally - 0.8–1.1. The color indicator is important for judging the normo-, hypo- or hyperchromia of erythrocytes.

Leukocytes - from 4.5 109 to 8.1 109/l (or 4.5–8.1 G/l). A decrease in the number of leukocytes below 4.0 G/l characterizes the development of leukopenia syndrome, and an increase above 9.0 G/l - leukocytosis syndrome (Table 1.3).

The erythrocyte sedimentation rate (ESR) is not a specific indicator for any disease, since it depends on qualitative and quantitative changes in blood plasma proteins, the amount of bile acids and pigments in the blood, the state of acid-base balance, blood viscosity and the number of red blood cells.

Normal ESR (using the micromethod modified by T.P. Panchenkov):

In men: 2–10 mm/h;

In women: 2–15 mm/h.

An increase in ESR is detected in various inflammatory processes, intoxications, acute and chronic infections, myocardial infarction, tumors, after blood loss and surgical interventions. A particularly pronounced increase in ESR is observed in hemoblastoses (myeloma, Waldenström's disease, etc.), malignant neoplasms, chronic active hepatitis, liver cirrhosis, tuberculosis, amyloidosis, collagenosis.

A decrease in ESR is observed with erythremia and symptomatic erythrocytosis, viral hepatitis, mechanical jaundice, hyperproteinemia, taking salicylates, calcium chloride.

Platelets - blood platelets, providing primary hemostasis, as well as activating plasma coagulation factors with antiheparin and antifibrinolytic activity.

Normal platelets: 200 109–400 109/l (200–400) 109/l

Anemia, or anemia, is a group of diseases characterized by a decrease in the content of Hb or Hb and the number of red blood cells per unit volume of blood (Table 1.4). Leukemia (leukemia) is a tumor systemic blood disease that occurs with damage to the bone marrow (Table 1.5).

Evaluation of pigment metabolism research

Bilirubin is a pigment formed during the oxidative breakdown of hemoglobin and other chromoproteins in the RES. Before entering the liver, the bilirubin formed after the breakdown of heme is combined with protein, therefore it gives an indirect reaction with the diazo reagent (needs preheating) - hence the name - indirect:

Unconjugated - unconjugated bilirubin. In the liver, bilirubin binds to glucuronic acid, and since this bond is fragile, the reaction with the diazo reagent is direct (direct - bound - conjugated bilirubin).

The normal content of total bilirubin in serum is from 5.13 to 20.5 µmol/l, of which 75-80% is indirect (unconjugated) bilirubin. Jaundice is visualized when bilirubin levels are above 34.2 µmol/L.

Increased bilirubin levels in the blood:

Damage to the liver parenchyma (infections, toxins, alcohol, medications);

Increased hemolysis of red blood cells;

Impaired flow of bile from the bile ducts to the intestines;

Loss of the enzyme unit that provides the biosynthesis of bilirubin glucuronide.

Table 1.3

Norms of absolute and relative (percentage) content individual species leukocytes (table unchanged)

Table 1.4

Picture of peripheral blood in anemia (table unchanged)

Table 1.5

Picture of peripheral blood in leukemia

Disease:	Indicators:
undifferentiated	The number of leukocytes varies widely - from leukopenia to leukocytosis, always blastemia (the appearance of blast cells in the peripheral blood or a blast content of more than 5% in the bone marrow). Characterized by leukemic failure (absence of intermediate maturing forms in the leukocyte formula. Anemia is normochromic or hyperchromic, erythrocytes (1.0–1.5) 1012/l; macroanisocytosis of erythrocytes; Hb reduced to 20–60 g/l. Thrombocytopenia (up to critical level).
Chronic lymphocytic leukemia	Severe leukocytosis with an absolute predominance of lymphocytes (80–95%) is possible, mainly small and medium-sized, but there may be prolymphocytes and lymphoblasts. Botkin-Gumprecht shadows (incompetent lymphocytes crushed during the preparation of a blood smear). Anemia is characteristic of exacerbation of the disease
Chronic myeloid leukemia	The number of leukocytes can vary from aleukemic and subleukemic indicators to severe hyperleukocytosis. IN leukocyte formula shift of granulopoiesis to metamyelocytes, myelocytes, promyelocytes and myeloblasts. All transitional forms of the granular series are present (there is no leukemic gap). A combined increase in eosinophils and basophils (eosinophil-basophil association) is one of the diagnostic signs of the initial stage of leukemia. The platelet count initially increases but then decreases
Polycythemia vera (erythremia, Vaquez disease)	Pancytosis is an increase in red blood counts in combination with neutrophilic leukocytosis and thrombocytosis. Increase in hemoglobin content - from 180 to 260 g/l

The study of bilirubin fractions is important for the differential diagnosis of parenchymal, obstructive and hemolytic jaundice. In case of hepatic jaundice (hepatitis, cirrhosis), two fractions of bilirubin are detected in the blood, usually with a sharp predominance of direct bilirubin. Significant indirect hyperbilirubinemia with parenchymal jaundice(over 34.2 µmol/l) indicates severe liver damage with impaired glucuronidation processes and is a poor prognostic sign. In obstructive jaundice, hyperbilirubinemia is mainly due to the direct fraction, but with severe forms congestive jaundice, the content of indirect bilirubin also increases.

With hemolytic jaundice - a sharp increase in indirect bilirubin due to its increased formation during hemolysis.

Blood proteins

The normal content of total blood protein is 60–80 g/l.

Hypoproteinemia (decreased total protein) occurs due to:

Insufficient protein intake (fasting);

Increased protein loss (with kidney disease, blood loss, neoplasms);

Protein synthesis disorders (liver disease).

Hyperproteinemia (increased total protein) occurs due to:

Dehydration (injuries, burns, cholera);

Paraproteinemia (myeloma, Waldenström's disease).

Using electrophoresis, proteins are divided into fractions:

Albumin (normally 50–70%) - hypoalbuminemia and hyperalbuminemia due to the same reasons as hypo- and hyperproteinemia.

Globulins (normally 11–21%) are acute phase proteins that reflect the intensity of inflammatory processes.

Main proteins acute phase are C-reactive protein, 1-glycoprotein, ceruloplasmin, haptoglobin.

Globulinemia is observed in chronic inflammatory diseases, tumors and their metastasis, injuries, heart attacks, rheumatism.

Globulins (normally 8–18%) increase with hyperlipoproteinemia (atherosclerosis, diabetes mellitus, hypothyroidism, nephrotic syndrome);

Globulins (normally 15–25%) increase due to the production of antibodies after an infectious disease, as well as in conditions that lead to depletion of the immune system: allergies, chronic inflammatory diseases, tumors and their metastasis, long-term therapy with steroid hormones, AIDS.

C-reactive protein (CRP) is an acute-phase protein, which is a product of tissue breakdown during various inflammatory and necrotic processes. In healthy people, the reaction to CRP is negative. The reaction is positive for rheumatism, septic endocarditis, myocardial infarction, diffuse connective tissue diseases, systemic vasculitis, tuberculosis, cancer, peritonitis, multiple myeloma.

Rheumatoid factor (RF) is an antibody that may belong to IgM class or IgG (as an exception - to the IgA class). The reaction is positive for rheumatism, infectious nonspecific polyarthritis, rheumatoid arthritis, systemic lupus erythematosus, periarteritis nodosa, liver cirrhosis, subacute infective endocarditis.

Fibrinogen (plasma factor 1) - synthesized in the liver. Normal plasma concentration (according to R.A. Rutberg’s method) is 5.9–11.7 µmol/l.

Decreased fibrinogen - liver failure, increased fibrin formation when fibrinolytic substances enter the bloodstream (amniotic fluid embolism, snake bite), with cachexia, B12-(folate) deficiency anemia, erythremia, severe toxicosis, shock. An increase in fibrinogen is observed in myocardial infarction, acute infections, diffuse connective tissue diseases, burns, and multiple myeloma.

Residual nitrogen

This is the nitrogen of compounds remaining in the blood after the precipitation of proteins.

Normal values: 14.3–28.6 mmol/l. Increase in residual nitrogen content:

Retention (in case of impaired renal function due to chronic glomerulonephritis, pyelonephritis, urolithiasis (KD), benign prostatic hyperplasia);

Productive (associated with increased formation of nitrogenous waste during fever and tumor disintegration).

Reduced residual nitrogen content:

In severe liver failure or liver necrosis.

Blood urea - 50% residual nitrogen; formed in the liver from ammonia and carbon dioxide.

Normal values:

Children under 14 years of age - 1.8–6.4 mmol/l;

Adults under 60 years of age - 3.5–8.3 mmol/l;

Adults over 60 years of age - 2.9–7.5 mmol/l.

Increase in urea - main feature renal failure, however, it occurs with increased protein breakdown and fluid loss.

Reduced urea - in case of liver diseases due to impaired urea synthesis, drug poisoning, low-protein diet. Blood creatinine - 7.5% of residual nitrogen; synthesized in the liver, kidneys, pancreas and transported to muscle tissue. Normal serum creatinine levels are 50–115 µmol/L, but there is significant age-related variation.

The concentration of creatinine in the blood is a fairly constant value, so endogenous creatinine clearance is used to estimate glomerular filtration. An increase in creatinine occurs when:

Acute and chronic renal failure;

Urolithiasis.

Uric acid is the end product of the breakdown of purine bases.

Normal values:

In men - 214–458 µmol/l;

In women - 149–404 µmol/l.

Hyperuricemia (increased uric acid levels) is observed with:

Leukemia, 12-deficiency anemia;

Polycythemia;

Acute infections;

Liver diseases;

Psoriasis, eczema;

Kidney diseases;

Long-term therapy with nonsteroidal and steroidal anti-inflammatory drugs.

Blood glucose is the main indicator of carbohydrate metabolism.

Normal fasting glucose values:

Plasma - 3.3 – 5.5 mmol/l;

Whole capillary blood - 3.88–5.55 mmol/l.

Hypoglycemia (decrease in glucose below 3.3 mmol/l in adults) occurs when:

Prolonged fasting;

Malabsorption, liver failure;

Impaired secretion of contrainsular hormones (hypopituitarism, chronic adrenal insufficiency);

Hypothyroidism;

Stroke;

Overdose of insulin and oral diabetic drugs;

Dietary disorders in patients with diabetes mellitus;

Insulinoma.

Hyperglycemia (increased glucose above 6 mmol/l in adults) occurs when:

Physiological conditions (nutritional, emotional);

Diabetes mellitus (provided the fasting level is 7 mmol/l or more and daily fluctuations after meals are up to 11 mmol/l); if diabetes mellitus is suspected and in risk groups, an oral glucose tolerance test is performed;

Hyperthyroidism;

Adrenocorticism;

Hypopituitarism.

Standards for interpreting analyses. The concept of reference values and reference interval.

The information obtained during laboratory analysis is based on the detection and / or measurement of certain components in clinical samples (biomaterial) of patients - analytes that are functionally or structurally related to a specific human organ or organ system. The most important component of any laboratory test is the interpretation of its result. In assessing the data obtained, a key role is played by establishing the difference between normal test results and pathology. In practice this is not difficult to do when clear deviation laboratory indicators from the values accepted as the norm. However, it is not always easy to divide most laboratory test results into “normal” and “pathological”, and therefore, in order to interpret them, it is necessary to compare the obtained data with the indicators established as the norm.

Normal test results (norm)- these are indicators detected in healthy people. However, in groups of the latter they can have different values, that is, the norm is individual. This is due to both individual physiological characteristics human body(features of metabolism, daily biological rhythms, functional state of certain organs and their systems), and differences in gender, age, physiological state. For example, during pregnancy, many biochemical indicators of a woman’s body change, so appropriate individual norms have been determined for pregnant women.

Normal values of laboratory parameters are determined during experimental clinical trials based on the results of measurements of the analyte of interest in a large population of healthy people, specially selected and grouped by age, sex or other biological and other factors. The obtained data lead to an average value, taking into account statistically possible standard deviations its size. In this regard, it is more correct to talk not about the “norm” of a laboratory indicator, but about the range in which normal (reference) values are located. Therefore, at present, the term “norm”, which has already become familiar in assessing the results of laboratory tests, is used less frequently. Instead they talk about reference (reference) values and the results obtained for a particular patient are compared with the so-called reference interval (range). This term is more accurate because it gives an idea of the lower and upper limits norms of a laboratory indicator, possible, statistically reliable limits of fluctuation (deviation) of its value and, at the same time, emphasizes the relativity of these data, the possibility of application only to a certain group of people.

Analysis decoding. Norm or pathology?

When establishing a reference range, mathematical and statistical approaches are used, according to which the values of the results of laboratory tests of a certain analyte of 95% of healthy people fall within the established interval. Accordingly, for 5%, the values of the analyzed indicators are outside the established range. In other words, in 5% of cases, “abnormal” laboratory parameters are detected in healthy people, which should be taken into account when interpreting the analysis. This is explained by a number of reasons.

Firstly, the division of the biological population of people into “sick” and “healthy” according to many laboratory indicators is very conditional. Being statistics, the limits normal values laboratory parameters may vary. Therefore, it happens that in healthy people, certain indicators that are the “norm” for them are not ultimately the “norm” for the majority of others, and therefore do not fall within the range of generally accepted reference values. In such a case, the limits of the reference range cannot serve in absolute terms health or illness.

On the other hand, the disease often develops unnoticed, manifesting itself as a gradual transition from small deviations in laboratory parameters to higher values as dysfunction and severity of the disease increases. In this regard, when deciphering tests and interpreting the results of laboratory tests, it becomes very important for the clinician to assess the dynamics of changes in a specific laboratory indicator in a specific patient. In doubtful cases, the main criterion for the presence or absence of the disease is clinical symptoms or the degree of its severity. If there are symptoms of the disease, additional laboratory tests are used for diagnosis using highly sensitive and specific tests that most significantly change their values against the background of the suspected disease.

Secondly, “healthy” and “sick” people actually belong to two different populations, and when these populations are mixed with each other, it is almost impossible to recognize each of them in the total mass. In addition, in different patients, the same indicator can not only take on different values, but also overlap the values of this indicator in healthy people. Moreover, for different indicators, various diseases, for different groups of patients, the magnitude of such a “crossover” can vary greatly: from too small, which can be neglected, to very significant, when a special approach and careful analysis of all data is required to classify the result as “normal” or “pathological”. The latter is extremely important to take into account when assessing the results of laboratory tests, since in this case not all values outside the normal range will indicate the presence of pathology. The range of values in which the laboratory parameters of “sick” and “healthy” individuals overlap is called the zone of uncertainty, or the “gray zone”. It exists for a number of laboratory techniques, but is most often found in the results of enzyme immunoassays. If a result falls into the “gray zone,” it cannot be unambiguously regarded as either normal or pathological and is considered doubtful. In such a case, the patient is usually recommended to repeat diagnostic test 2 – 4 weeks after receiving an indeterminate result.

And finally, an indicator lying in the reference interval cannot always be considered normal, since the range of many of them is quite wide. For example, the normal hematocrit (Ht) value in men varies from 42 to 52%. Massive blood loss can lead to a drop in this indicator from 52 to 42%, while the value of 42% remains within the range of reference values, and therefore may not cause alarm to doctors. However, in a certain situation, for a particular patient, such a decrease in hematocrit can not only be clinically significant, but also be critical.

Thus, results within the reference range are not always the norm. And, on the contrary, results that go beyond the reference values are not always a pathology, but only a significant prognostic sign that can signal a possible pathological process. In this regard, in laboratory diagnostics an approach is becoming increasingly widespread when the most significant and adequate reference values for each individual patient should be considered the stable results of his laboratory tests obtained over several years. Even now, experts all over the world are inclined to believe that it is necessary to “lower” the importance of reference intervals, moving away from treating them as some kind of “absolute” criterion for assessing a laboratory result. This circumstance in no way reduces the importance of laboratory research. They stay the most important tool diagnostics of pathological conditions, monitoring the course of diseases, identifying the preclinical stage of diseases during screening examinations, and also largely determine the further tactics of diagnostic procedures and making treatment decisions. However, this approach directs the clinician to a more cautious use of reference values in the assessment of “normal” and “pathological” results, indicating the need for their interpretation taking into account possible biological variation in the population, taking into account the data clinical picture and other types of research in the aggregate, as well as those factors that may influence the results of laboratory research.

Reference ranges

Currently, reference values have been established for many laboratory parameters. The results of some types of tests are given to the patient in the form of “yes” or “no”. This type of research is qualitative. For example, a positive result for antibodies to a certain infection indicates the presence of these antibodies in the patient’s blood and may indicate infection. In the case where the research was quantitative, the result is given in the form of a digital value indicating the units of measurement and the corresponding reference range on the form. For example, the results of a biochemical study to determine the level of C-reactive protein (CRP), which is a marker of inflammation, may look like this: 0.4 mg/l, reference values: 0 – 6 mg/l. From the above example it is clear that the result obtained is within the established reference range. For most laboratory indicators, the range of reference values is indicated taking into account the patient’s gender and/or his belonging to a certain group. age group. For example, reference values for serum creatinine for children under 1 year of age are 18 - 35 µmol/l, for children from one to 14 years old - 27 - 62 µmol/l, and for persons over 14 years old - 62 - 115 µmol/l for males and 53 - 97 µmol/l for females.

The influence of age and gender on the reference range is significant for many laboratory tests. For example, the concentration of alkaline phosphatase, a key enzyme secreted by cells bone tissue, increases in proportion to the rate of formation of its new cells. Therefore, in children and adolescents, high levels of this enzyme are not only normal, but also desirable, since they are associated with active bone formation and growth. On the contrary, a high level of alkaline phosphatase in an adult may indicate developing osteoporosis, metastases of bone tumors or other pathological processes. The exception is pregnant women, who are characterized by a physiological increase in the activity of this enzyme, especially in the third trimester of pregnancy.

Why may reference ranges vary between laboratories?

Different diagnostic laboratories use different types of laboratory equipment to perform analysis, for example, biochemical and immunochemical analyzers, the range of which is currently very wide, work on reagents from different manufacturers, and in addition, they may use research methods that are different from other laboratories. In this regard, each laboratory indicates on the results form its ranges of reference values, when establishing which it is guided, of course, by generally accepted standards, but taking into account individual characteristics of your work: the specifics of the equipment used, the methods of analysis and units of measurement used. That is why the ranges of reference values for the same laboratory test can vary according to data from different diagnostic laboratories, and there is no such thing as a “single” reference range. When assessing the results of laboratory tests, the attending physician must first of all refer to the range of reference values indicated on the form of the laboratory in which the analysis was performed. In order for the interpretation of the results to be correct and their comparability to be observed, especially in the case of repeated studies, for example, when monitoring therapy or dynamic assessment of the patient’s condition, it is advisable to conduct studies using the same method, in the same laboratory and, if possible, other things being equal.

Factors influencing laboratory results

Modern methods of clinical laboratory testing are characterized by high sensitivity and specificity, and therefore their results, reflecting the patient’s health status, can serve as the basis for the attending physician to make important clinical decisions. At the same time, both clinicians and patients must understand that there are a number of non-pathological factors that can, to a certain extent, influence the results of laboratory tests, distorting the objective picture of the patient’s health status. Some of these factors can only be controlled through the efforts of laboratory specialists, minimizing their possible negative impact on the final result of laboratory research. Such factors include, for example, the conditions and method of collecting biological material, delivery and storage of samples, and the correctness of their identification in the laboratory. However, only the patient himself or his attending physician, who must inform the patient about the correct preparation for a certain type of laboratory test, can minimize the negative impact of many other factors that affect the accuracy of the final result of a laboratory test. Compliance with the doctor’s instructions will allow the analysis to be carried out as close as possible to the general requirements, for example, the need to donate blood on an empty stomach, and thereby bring the results of the study as close as possible to the reference ones for this group of patients.

What factors can influence the results of laboratory tests? First of all, it should be noted the sensitivity of many laboratory tests to the time interval associated with the patient’s intake of food in general or individual products in particular, as well as with the characteristics of his eating behavior, for example, following a diet (meat or vegetarian), drinking coffee and alcohol. For example, high blood sugar may be related to a recent meal rather than diabetes. Eating shortly before the test will affect the results of lipid profile tests, insulin and C-peptide levels. In this regard, to obtain accurate test results, it is recommended to donate blood in the morning on an empty stomach, usually no less than 8 and no more than 14 hours after the last meal. On the eve of the study, food overload should be avoided.

High liver enzyme levels may be a result of recent or frequent alcohol use. Caffeine may cause an increase in plasma concentrations of catecholamines and renin. Smoking sometimes causes borderline increases in the levels of some tumor markers.

The results of laboratory tests may be affected by taking vitamins and nutritional supplements, as well as medications. At the same time, the effects of medications can be multidirectional. They can not only change physiological processes in the body, but also chemically interfere (interact) with the test analyte under conditions in vitro. An example of the effect of drugs at a physiological level is the increase in liver enzymes under the influence of hepatotoxic drugs. Drugs that affect plasma volume may cause changes in the concentrations of proteins, urea nitrogen, iron and calcium. An example of another influence is nonspecific binding reactions of some drug metabolites with individual components of the reaction mixture, for example, polyclonal antibodies during immunoassays, as a result of which an erroneous result may be obtained. In this regard, a patient taking any medications should consult with a doctor about the advisability of conducting a laboratory test while taking medications or the possibility of stopping them before the study.

Among the factors influencing the results of laboratory tests is physical activity. Physical stress leads to a volumetric shift between the vascular bed and the intercellular space, loss of fluid through sweat and, as a consequence, a change in the concentration of certain analytes: hormones or enzymes. Therefore, visiting, for example, the gym on the eve of a laboratory test is undesirable. Heavy physical activity can cause an increase in the level of certain enzymes (ALT, AST, LDH, creatine kinase), a change in the level of various blood substrates (glucose, urea, etc.), and an increase in protein excretion in the urine. In addition, in people who are actively involved in sports for a long time, for example, long-distance running or weightlifting, testosterone and luteinizing hormone (LH) levels may be slightly increased.

A general recommendation for preparing for the study is to advise, after arriving at the laboratory, to rest (preferably sit) for 10 to 20 minutes before taking blood samples. This is also due to the fact that the results of some laboratory tests may be influenced by the body position of the subject at the time of the test, as well as the emotional state of the person before and during the study. For example, a change in body position from a lying position to a sitting or standing position causes vascular contraction, and a change in position from a sitting to a lying position causes a shift of water and electrolytes in the tissue, leading to blood concentration. As a result, the levels of total protein, albumin, lipids, iron and calcium in the serum or plasma change upward.

Emotional stress can cause significant increases in cortisol, ACTH and glucose levels. Among other things, stress is combined with an increase in the concentrations of albumin, fibrinogen, insulin, lactate and cholesterol. That is why it is so important, if possible, to exclude psycho-emotional stress on the eve of the study and try not to worry during the process of taking a biological sample.

Temporary changes in some laboratory parameters can be caused by physical procedures and instrumental examinations(eg, prostate biopsy before PSA test). In such cases, it is recommended to postpone laboratory testing for several days.

For a number of hormonal studies, it is important to take into account the phase of the menstrual cycle in women, and therefore you should check with your doctor in advance about the optimal days for donating blood to determine the level of FSH, LH, inhibin B, prolactin, progesterone, estradiol and some other hormones.

The time of day when taking the sample is especially important if it is necessary to determine the level of cortisol, thyroid-stimulating hormone(TSH) and some other analytes. It should be borne in mind that reference values - the boundaries of the “norm” of laboratory parameters, usually reflect statistical data obtained in standard conditions when taking blood in the morning.

Thus, there are a number of reasons why test results may fall outside the established reference range, even if a person is completely healthy. Therefore, if the patient is aware of any special circumstances that could affect the test results, you should inform your doctor about them. Don't expect him to figure them out on his own. After all, a result that does not correspond to the “norm” is not necessarily a sign of a disease, and therefore the doctor needs to understand its possible cause. It is possible that this is precisely the case when the result obtained falls within that statistically significant 5% in which the laboratory parameters of healthy people fall outside the reference range. Sometimes some “abnormal” results can return to normal on their own, especially if they were on the border of the reference values. In addition, there are not many diseases that can be diagnosed with just one single test.

The above examples indicate that for an adequate assessment of the results of laboratory tests, as well as the subsequent adoption by a doctor of correct clinical decisions regarding the patient based on them, it is necessary A complex approach, taking into account all the variety of factors that can influence the accuracy and correctness of the data obtained. Clinical conclusions and decisions made based on the results of laboratory tests will be correct only if the various preanalytical and analytical factors in sufficiently standardized and most fully taken into account. It is very important that the patient is able to comply with all the necessary recommendations for preparing for laboratory tests, and the attending physician, when interpreting the data obtained, takes into account possible influence on the results of the study of non-pathological factors that took place, and also comprehensively assessed the results obtained, taking into account the clinical picture and data from other types of studies.

Laboratory diagnostic specialists, if necessary, are always ready to answer questions about the results obtained, provide additional special information and clarifications, or provide advice in difficult cases.

Laboratory results are subject to biological and analytical variations. If analytical variation depends on the test conditions, then the magnitude of biological variation depends on a whole complex of factors. The general biological variation of the studied indicators is due to intra-individual variation observed in the same person as a result of the influence of biological rhythms (different times of day, year), and inter-individual variation caused by both endogenous and exogenous factors, the main of which are presented in Fig.

■ Physiological patterns (the influence of race, gender, age, body type, nature and volume of habitual activity, nutrition).

■ Environmental influence (climate, geomagnetic factors, time of year and day, composition of water and soil in the habitat, social and living environment).

Rice. Sequence of evaluation of laboratory test results

■ Exposure to occupational and household toxic substances [alcohol, nicotine, drugs) and iatrogenic influences (diagnostic and therapeutic procedures, drugs).

■ Conditions for taking a sample (food intake, physical activity, body position, stress during sample taking, etc.).

■ Method of collecting blood (method of collection, means and utensils, preservatives, etc.).

■ Incorrect (timing) collection of material.

■ Conditions (temperature, shaking, light influence) and time of transportation of biomaterial for research in the laboratory.

Rice. Factors influencing biological variation [Garanina E.N., 1997].

Let's consider the influence of the most important factors on the results of laboratory tests.

the concentration of triglycerides (TG), free fatty acids without significant changes in the concentration of cholesterol (CS).

Eating fatty foods can increase potassium, TG, and alkaline phosphatase concentrations. The activity of alkaline phosphatase in such cases may especially increase in people with O- or B-blood group. Physiological changes after eating fatty foods in the form of hyperchylomicronemia can increase the turbidity of the blood serum (plasma) and thereby affect the results of optical density measurements. An increase in the concentration of lipids in the blood serum may occur after the patient has consumed butter, cream or cheese, which will lead to false results and require re-analysis.

Consumption of large amounts of meat, that is, foods high in protein, can increase the concentrations of urea and ammonia in the blood serum, and urate in the urine. Foods with a high ratio of unsaturated to saturated fatty acids can cause a decrease in serum cholesterol concentrations, and foods rich in purines cause an increase in urate concentrations. Bananas, pineapples, tomatoes, avocados are rich in serotonin. If they are consumed 3 days before a urine test for 5-hydroxyindoleacetic acid, even in a healthy person its concentration may be increased. Drinks rich in caffeine increase the concentration of free fatty acids and cause the release of catecholamines from the adrenal glands. Drinking alcohol increases the concentration of lactate, uric acid and TG in the blood.

The general rule for eliminating the influence of food intake on the results of laboratory tests is to draw blood after a 12-hour fast.

The influence of drugs on the results of laboratory tests can be of two types.

■ Physiological effect in vivo (in the patient’s body) of drugs and their metabolites.

■ Influence in vitro (on the chemical reaction used to determine the indicator) due to the chemical and physical properties of the drug (interference).

Interference can be caused by the presence of both endogenous and exogenous substances in the biomaterial sample. The main endogenous interfering factors include the following.

■ Lipemia, which distorts the results of a number of colorimetric and nephelometric research methods (especially when studying phosphorus, total bilirubin, uric acid, total protein, electrolytes).

■ Paraproteinemia, which causes changes in the results of determining phosphates, urea, CK, LDH, and amylase by certain methods.

Body position during blood sampling also affects a number of indicators. Thus, a patient’s change from a lying position to a sitting or standing position leads to hydrostatic penetration of water and filtered substances from the intravascular space into the interstitial space. Substances with a large molecular weight (proteins) and blood cells with substances associated with them do not pass into the tissue, so their concentration in the blood increases (enzymes, total protein, albumin, iron, bilirubin, cholesterol, TG, drugs associated with proteins , calcium). The concentration of Hb, Ht, and the number of leukocytes may increase.

■ For burns that occupy a large surface area of the patient’s body.

■ If the patient has very small veins or their limited accessibility.

■ If the patient is severely obese.

■ With an established tendency to venous thrombosis.

■ In newborns.

The time and conditions of transportation of biological samples also play an important role in ensuring the quality of laboratory research results. When delivering material to the laboratory, it is always necessary to remember the characteristics of some samples. For example, when collecting arterial blood for gas analysis, the blood container should be well sealed, immersed in ice water and delivered to the laboratory as soon as possible, since glycolysis in red and white blood cells causes a decrease in pH if the sample is kept at room temperature for approximately 20 minutes . These requirements must also be observed when studying capillary blood, which is collected into heparinized capillaries. Blood for testing for adrenocorticotropic hormone (ACTH), angiotensin I, II, renin should also be placed on ice immediately after collection and delivered to the laboratory as quickly as possible.

Table 1-1. Delivery times for samples to the laboratory

The influence of various factors on the results of laboratory tests

Laboratory tests are often more sensitive indicators of a person's condition than how they feel. The test results reflect physicochemical characteristics of the test sample and provide objective diagnostic information in digital terms. Important decisions about patient management strategy are often based on small changes in laboratory data. That is why the role of laboratory tests, as well as the range and number of studies required in the process of diagnosing and treating diseases, is constantly increasing. However, from the practice of any diagnostic laboratory it is known that the results they obtain are not always correct. This is due to the presence of a large number of non-pathological factors that can influence final results laboratory data.

As our work experience shows, the majority of unsatisfactory results obtained are associated with errors made during the analysis. The appearance of random and systematic errors at any stage of analysis will reduce the reliability of laboratory results and, as a result, complicate the diagnosis correct diagnosis and providing adequate treatment.

PRE-ANALYTICAL (PRE-LABORATORY) STAGE includes all stages from the appointment of an analysis by a clinician until the sample arrives at the laboratory at the workplace, namely: the appointment of an analysis, the collection of biological material, its processing and delivery to the laboratory. Errors arising at the non-laboratory stage of analysis account for from 70% to 95% of their total number. They may turn out to be irreparable and completely devalue the entire course of ongoing research.

Therefore, the correct organization of the preanalytical stage should become an integral part of any quality assurance system for laboratory analysis.

When receiving, processing and delivering samples to the laboratory, the following factors should be kept in mind, which may or may not be avoidable. Laboratory results are subject to biological and analytical variations. If analytical variation depends on the test conditions, then the magnitude of biological variation depends on a whole complex of factors. The general biological variation of the studied indicators is due to intra-individual variation observed in the same person as a result of the influence of biological rhythms (different times of day, year), and inter-individual variation caused by both endogenous and exogenous factors.

Physiological patterns (the influence of race, gender, age, body type, nature and volume of habitual activity, nutrition);
Environmental influence (climate, geomagnetic factors, time of year and day, composition of water and soil in the habitat area, social and living environment);
Exposure to occupational and household toxic substances (alcohol, nicotine, drugs) and iatrogenic influences (diagnostic and therapeutic procedures, medications);
Conditions for taking a sample (food intake, physical activity, body position, stress during sample taking, etc.);
Method of collecting blood (method of collection, means and utensils, preservatives, etc.);
Incorrect (timing) collection of material;
Conditions (temperature, shaking, influence of light) and time of transportation of biomaterial for research in the laboratory.

Let's consider the influence of the most important factors on the results of laboratory tests.

EATING

Diet, composition of food intake, breaks in its intake have a significant impact on a number of laboratory test indicators. After a meal, the content of individual metabolic products in the blood may increase or undergo changes as a result of post-absorption hormonal effects. Determination of other analytes may be difficult due to turbidity caused by chylomicronemia in postprandial blood samples.

After 48 hours of fasting, the concentration of bilirubin in the blood may increase. Fasting for 72 hours reduces blood glucose concentrations in healthy people to 2.5 mmol/l, increases the concentration of triglycerides, free fatty acids without significant changes in cholesterol concentrations. Long-term fasting (2 - 4 weeks) can also affect a number of laboratory parameters. The concentration of total protein, cholesterol, triglycerides, urea, lipoproteins in the blood decreases; excretion of creatinine and uric acid by the kidneys in the urine increases. Prolonged fasting is closely associated with decreased energy expenditure. As a result, the concentration of thyroid hormones in the blood - total thyroxine and, to an even greater extent, triiodothyronine - decreases. Fasting also leads to increased levels of cortisol and dehydroepiandrosterone sulfate in serum samples.

Eating fatty foods may increase potassium, triglyceride, and alkaline phosphatase concentrations. The activity of alkaline phosphatase in such cases may especially increase in people with O- or B-blood group.

Physiological changes after eating fatty foods in the form of hyperchylomicronemia can increase the turbidity of the blood serum (plasma) and thereby affect the results of optical density measurements. An increase in the concentration of lipids in the blood serum may occur after the patient has consumed butter, cream or cheese, which will lead to false results and require re-analysis.

Certain types of food and dietary patterns can affect a number of serum and urine parameters. Consumption of large amounts of meat, that is, foods high in protein, can increase the concentrations of urea and ammonia in the blood serum, and the amount of urate (calcium salts) in the urine. Foods with a high ratio of unsaturated to saturated fatty acids can cause a decrease in serum cholesterol concentrations, and meat foods cause an increase in urate concentrations. Bananas, pineapples, tomatoes, avocados are rich in serotonin. If they are consumed 3 days before a urine test for 5-hydroxyindoleacetic acid, even in a healthy person its concentration may be increased. Drinks rich in caffeine increase the concentration of free fatty acids and cause the release of catecholamines from the adrenal glands and brain (the concentration of catecholamines in the blood serum increases). Caffeine can increase plasma renin activity. Drinking alcohol increases the concentration of lactate, uric acid and triglycerides in the blood. Elevated levels of total cholesterol, uric acid, gamma-glutamyl transpeptidase and an increase in mean erythrocyte volume may be associated with chronic alcoholism.

A salt-free diet can lead to an increase in aldosterone levels by 3-5 times. The concentration of bilirubin after a 48-hour fast can increase by 2 times, after eating it decreases by 20–25%; changes in bilirubin levels during the day can reach 15–30%.

PHYSICAL EXERCISE

The physical activity status of the subject has a great influence on the results.

Physical activity can have both transient and long-term effects on various parameters of homeostasis. Transient changes include first a decrease and then an increase in the concentration of free fatty acids in the blood, an increase in the concentration of ammonia by 180% and lactate by 300%, an increase in the activity of creatine kinase, AST, LDH. Physical exercise affects hemostasis: it activates blood coagulation and the functional activity of platelets. Changes in these indicators are associated with activation of metabolism and they usually return to their original (before physical activity) values soon after cessation of physical activity. However, the activity of some enzymes (aldolase, CK, AST, LDH) may remain elevated for 24 hours after 1 hour of intense physical activity. Prolonged physical activity increases the concentration of sex hormones in the blood, including testosterone, androstenedione and luteinizing hormone (LH).

With prolonged strict bed rest and restriction of physical activity, urinary excretion of norepinephrine, calcium, chlorine, phosphates, ammonia, and alkaline phosphatase activity in the blood serum increase.

EMOTIONAL STRESS

The impact of mental stress (fear of blood collection, fear of surgery, etc.) on laboratory test results is often underestimated. Meanwhile, under its influence, transient leukocytosis is possible; decreased iron concentration; increased levels of catecholamines, aldosterone, cortisol, prolactin, angiotensin, renin, growth hormone, TSH and increased concentrations of albumin, glucose, fibrinogen, insulin and cholesterol. Severe anxiety accompanied by hyperventilation causes an acid-base imbalance (ABS) with increased concentrations of lactate and fatty acids in the blood.

GENDER OF THE PATIENT

For a number of clinical, chemical and hematological parameters, there are statistically significant differences between the sexes. In particular, this applies to the levels of steroid and glycoprotein hormones (progesterone, estradiol, testosterone, 17-OH progesterone, LH, FSH, prolactin), transport proteins (SSG, TSG) and other biologically active compounds (TG). There is extensive information on this issue in the methodological literature, in addition, it can be found in most instructions for using diagnostic kits. However, it should be noted that the reference intervals given in the literature should be considered as indicative only. This is due to the presence of design features of sets from different manufacturing companies, as well as regional and racial differences in the composition of the population. Therefore, it is recommended that each laboratory set its own values. normal levels studied indicators using those types of kits that are regularly used in routine practice.

PATIENT AGE

The concentration of a whole range of analytes depends on the age of the patient and can vary significantly from birth to old age. Age-related changes are most pronounced for some biochemical parameters (hemoglobin, bilirubin, alkaline phosphatase activity, low-density lipoprotein content, etc.) as well as for a number of analytes determined by immunochemical methods. These include sex steroid and glycoprotein hormones, thyroids, ACTH, aldosterone, renin, growth hormone (somatotropic), parathyroid hormone, 17-hydroxyprogesterone, dehydroepiandrosterone, PSA, etc. It is desirable that each laboratory have age standards for each of the indicators being studied, which will allow a more accurate interpretation of the results.

PREGNANCY

When interpreting the results of laboratory tests in pregnant women, it is necessary to take into account the gestational age at the time the sample is taken. During physiological pregnancy, the average plasma volume increases from approximately 2600 to 3900 ml, and in the first 10 weeks the increase may be insignificant, and then there is an increasing increase in volume by the 35th week, when the specified level is reached. Urine volume may also physiologically increase by up to 25% in the 3rd trimester. In the last trimester, there is a 50% physiological increase in glomerular filtration rate.

Pregnancy is normal physiologicalprocess, which is accompanied by significant changes in the production of steroid, glycoprotein and thyroid hormones, transport proteins (DES, TSG), ACTH, renin, as well as in a number of biochemical and hematological parameters. Therefore, for the correct interpretation of the results, it is important to accurately indicate the gestational age when the blood sample under study was taken.

During screening birth defects fetal development according to laboratory indicators, it should be borne in mind that the diagnostic sensitivity and specificity of this type of study will largely be determined by the combination of selected immunochemical markers. It should be different for different stages fetal development. For example, for the first trimester of pregnancy, the most preferable is the determination of AFP, free 6-subunit of hCG and pregnancy-associated protein A (PAPPA), and for the second trimester - AFP, total hCG and free estriol. All of these types of analysis must be carried out during strictly recommended periods of pregnancy, and each laboratory engaged in screening studies must have its own constantly updated and replenished database of median levels of the markers studied for each week of pregnancy.

MENSTRUAL CYCLE

Statistically significant changes in concentration can be caused by fluctuations hormonal levels during menstruation. Thus, the concentration of aldosterone in plasma is determined to be twice as high before ovulation than in the follicular phase. Similarly, renin may exhibit a preovulatory increase.

The menstrual cycle is normal physiological process, which is accompanied by significant changes in the production of sex and thyroid hormones, transport proteins, ACTH, renin, as well as in a number of biochemical and hematological parameters. To correctly interpret the results, it is important to accurately indicate the day of the menstrual cycle when the blood sample under study was taken.

BIOLOGICAL RHYTHMS

There are linear chronobiological rhythms - such as the patient's age, cyclical rhythms - such as circadian and seasonal, and other biological cycles - such as the menstrual cycle.

Circadian rhythms of the analyte, i.e. changes in its concentration during the day are most pronounced in cortisol, ACTH, aldosterone, prolactin, renin, TSH, parathyroid hormone, testosterone, etc. Deviations of concentrations from the average daily values can reach 50%-400%, and this factor must be taken into account .

Daily fluctuations in the content of some analytes in blood serum

	Maximum concentration(Times of Day)	Minimum concentration (time of day)	Amplitude (% of daily average)

Cortisol
Testosterone



Prolactin
Aldosterone

Adrenalin

For example, circadian rhythm Cortisol may cause unreliable results on a glucose tolerance test if it is taken in the afternoon.

In order not to complicate the process of interpreting the results, sampling for analysis should be carried out strictly at a certain time of day, usually between 7:00 and 9:00 am. It should be borne in mind that the reference intervals of most tests given in the reference literature are established specifically for this period of time.

When conducting special studies, for example, when establishing an individual circadian rhythm of hormone secretion, several samples of the analyzed material are taken during the day. The documents accompanying such samples must indicate the exact time at which each sample was taken.

Individual rhythms of sleep, eating, and physical activity can be superimposed on the circadian rhythm, which should not be confused with truly daily fluctuations. In order to exclude individual rhythms when determining the level of analytes secreted in portions (renin, vasopressin, testosterone, prolactin, etc.), you can use a mixed sample obtained from three blood samples taken at intervals of 2-3 hours. In some cases, seasonal influences must be taken into account. For example, triiodothyronine content is 20% lower in summer than in winter.

TAKEN MEDICINES

Reception can be reflected in the quantitative content in the body of a number of analyzed indicators. For example, TSH levels decrease with dopamine treatment, the concentration of total and free fractions of thyroid hormones will change with the administration of furosemide, danazol, amiodarone and salicylates, and the use of some antiulcer drugs can increase prolactin levels in men.

The presence of drugs in biological material - for example, contraceptives, salicylates, androgens, etc. - can in a specific (cross-reaction) or non-specific manner (interference) affect the results of laboratory tests when determining the concentration of steroid and thyroid hormones, as well as specific binding proteins in the blood. When determining the duration of bleeding according to Duque, taking aspirin-containing drugs should be discontinued 7 to 10 days before the study. If this is not done, you may get a pathological test result. Therefore, carrying out drug therapy, which can distort the results of the analysis, should be prescribed after taking blood samples.

When conducting drug monitoring, the exact time of blood collection is a very important parameter for the correct interpretation of study results.

A wide range of drug interference in laboratory studies has been discussed in many reviews and books. To exclude the possibility of obtaining false results due to the use of medications, it is recommended to consult with clinicians and also use the appropriate reference books.

When preparing subjects for biochemical studies, the following approaches were adopted: medications that interfere with the determination of components are excluded before taking biomaterial, if they are not given for health reasons; morning medication is taken only after taking biomaterial; Blood sampling for diagnostic purposes is carried out before infusion of drugs and solutions. Contamination of laboratory samples by infusion solutions is the most common and frequently encountered form of preanalytical interference in hospitals. It is recommended to inform the laboratory about when and what kind of infusion was given to the patient, and when the blood sample was drawn.

A blood sample should never be collected from a vessel located proximal to the infusion site. Samples should be taken from the other arm, from a vein that is not being infused.

The influence of drugs on the results of laboratory tests can be of two types:

Physiological influence in vivo(in the patient’s body) drugs and their metabolites;
Influence in vitro(to the chemical reaction used to determine the indicator) due to the chemical and physical properties of the drug (interference).

Interference can be caused by the presence of both endogenous and exogenous substances in the biomaterial sample. The main endogenous interfering factors include the following:

Hemolysis, i.e. destruction of red blood cells with the release of a number of intracellular components into the liquid part of the blood (hemoglobin, LDH, potassium, magnesium, etc.), which changes the true results of determining the concentration/activity of such blood components as bilirubin, lipase, CK, LDH, potassium, magnesium, etc. ;
Lipemia, which distorts the results of a number of colorimetric and nephelometric research methods (especially when studying phosphorus, total bilirubin, uric acid, total protein, electrolytes);
Paraproteinemia, causing changes in the results of determining phosphates, urea, CK, LDH, and amylase by certain methods.

Identifying drug interference is one of the tasks of a clinical laboratory diagnostics doctor. An important step in solving this problem is contacting the clinician to clarify the nature of the medications the patient is taking.

SMOKING

Smokers may have increased concentrations of carboxyhemoglobin, plasma catecholamines and serum cortisol. Changes in the concentrations of these hormones often lead to a decrease in the number of eosinophils, while the content of neutrophils, monocytes and free fatty acids increases. Smoking leads to an increase in hemoglobin concentration, red blood cell count, mean erythrocyte volume (MCV) and a decrease in white blood cell count. An increase in gammaglutamyltransferase activity by 10% was found when consuming 1 pack of cigarettes per day; Possible doubling of activity compared to reference values upon consumption more cigarettes.

DIAGNOSTIC AND TREATMENT MEASURES

The following diagnostic and treatment measures may influence the results of laboratory tests:

Surgical interventions;
Infusions and transfusions;
Punctures, injections, biopsies, palpation, general massage;
Endoscopy;
Dialysis;
Physical stress (eg, ergometry, exercise, ECG);
Functional tests (eg, oral glucose tolerance test);
Taking radiopaque and medicinal substances;
Ionizing radiation.

For example, PSA levels may be elevated for several days after prostate massage or catheterization. Bladder. Any manipulation of the mammary gland or thermal procedures (for example, a sauna) lead to a significant increase in prolactin levels. To prevent such interference, sampling should be performed before performing diagnostic procedures that may bias the test results. Vaginal bleeding before the blood sample is taken may influence the screening result: bleeding may increase the level of AFP in the mother's blood. In these conditions, it is recommended to delay the test for ~ one week after the bleeding has stopped.

SAMPLING FREQUENCY

Repeated blood sampling is widely used in dynamic studies - when conducting stimulation tests, to assess the effectiveness of treatment, when predicting the outcome of a disease, during drug monitoring, as well as in a number of other cases. The sampling intervals, in addition to the specific objectives of the study, should be determined taking into account the following factors:

The biological half-life of the analyte being determined. For example, to assess PSA levels in the postoperative period, blood sampling for testing should be carried out no earlier than 10-14 days after surgery;
Pharmacokinetic properties of drugs during therapeutic drug monitoring. For example, blood sampling to determine cyclosporine A should be done immediately before taking the next dose, and for cardiac glycosides - 4 hours after administration of the drug.
Dynamics of changes in analyte concentration during normal or pathological processes (pregnancy monitoring, diagnosis and monitoring of tumor and infectious diseases, etc.). Typically, individual fluctuations in the levels of the studied analytes can be very significant (free estriol, hCG, AFP, etc.). In these cases, the average normal values or ranges are not sufficiently informative for making a diagnosis. Instead, the median values of normal concentrations are used.

When monitoring tumor diseases, as well as to assess the effectiveness of treatment, individual baseline levels of tumor markers before the start of therapy are used as a reference point. Subsequent blood draws are carried out at intervals strictly determined by clinicians. The same principle is used in diagnosis and treatment infectious diseases- identification specific antibodies to the pathogen and the dynamics of their levels during treatment.

When urine samples are stored at room temperature, up to 40% of glucose may be lost after 24 hours of storage.

POSITION OF THE PATIENT'S BODY WHEN TAKING BLOOD

The patient's body position also affects a number of indicators. The transition from a lying position to a sitting or standing position leads to hydrostatic penetration of water and filterable substances from the intravascular space into the interstitial space. Substances with a large molecular weight (proteins) and blood cells with substances associated with them do not pass into the tissue, so their concentration in the blood increases (enzymes, total protein, albumin, iron, bilirubin, cholesterol, TG, drugs; protein-related , calcium). The concentration of hemoglobin, hematocrit, and the number of leukocytes may increase. Blood sampling for the determination of a number of analytes - such as aldosterone, epinephrine, norepinephrine, atrial natriuretic peptide, as well as to assess plasma renin activity - should be carried out in the supine and/or standing position with the patient at rest. The referral must include a special note indicating the time and conditions under which the sample was obtained.

PLACE AND TECHNIQUE FOR BLOOD COLLECTION

The location and technique of blood collection can also have a significant impact on the results of laboratory tests (for example, applying a tourniquet for a period of time of more than 2 minutes when collecting blood from a vein can lead to hemoconcentration and an increase in the concentration of proteins, coagulation factors, and the content of cellular elements in the blood). The best place to collect blood for testing is the ulnar vein. It should also be noted that venous blood is the best material not only for determining biochemical, hormonal, serological, immunological parameters, but also for general clinical research. This is due to the fact that the currently used hematological analyzers, with the help of which general clinical blood tests are carried out (cell counting, determination of hemoglobin, hematocrit, etc.), are designed to work with venous blood, and for the most part in the countries where they are produced, they are certified and standardized to work only with venous blood. Calibration and control materials produced by companies are also intended for calibration of hematology analyzers using venous blood.

In addition, when collecting blood from a finger, a number of methodological features are possible that are very difficult to standardize (cold, cyanotic, swollen fingers, the need to dilute the test blood, etc.), which leads to significant variations in the results obtained and, as a consequence, to the need for repeated research to clarify the result.

For general clinical examination, it is recommended to take blood from a finger in the following cases:

For burns that occupy a large surface area of the patient’s body;
If the patient has very small veins or their low accessibility;
If the patient is severely obese;
With an established tendency to venous thrombosis;
In newborns.

Arterial puncture for blood sampling is rarely used (mainly to study the gas composition of arterial blood).

OTHER FACTORS

Among other factors influencing the results of research, race, geographic location of the area, altitude above sea level, and ambient temperature are important.

For example; AFP levels are higher in black women compared to Caucasian women. GGT activity is approximately twice as high in African Americans compared to whites.

How to properly prepare for research in a clinical diagnostic laboratory

BLOOD TEST (CLINICAL, BIOCHEMICAL, IMMUNOENzyme)

GLUCOSE TOLERANCE TEST (SUGAR CURVE)

An oral glucose tolerance test is performed if clinical symptoms There are no diabetes mellitus, and the fasting blood glucose level is below the pathological level and is within the physiological norm(You must first conduct a fasting blood glucose test).

Purpose of the test– determine the efficiency of the insulin secretory mechanism of the pancreas and the glucose distribution system of the body. It is necessary to prepare for this test by changing your diet and taking medications at least 3 days before the test. It is very important to follow the instructions below exactly, as only then will valuable test results be obtained:

The amount of carbohydrate in food must be at least 125 grams per day for 3 days before the test;
You should not eat anything for 12 hours preceding the start of the test, but in no case should you fast for more than 16 hours;
Don't let yourself physical exercise within 12 hours before the test and during the test.

Test procedure. The study is performed twice with an interval of 2 hours. In the morning, on an empty stomach, blood is drawn for glucose. The patient is then given a certain amount of glucose (depending on body weight) dissolved in warm water. The load should be taken slowly, not in one gulp, but not longer than 5 minutes. During this time, an adequate physiological response to taking large amounts of carbohydrates is formed. After taking the load, blood is taken again for glucose after 2 hours. Instead of glucose, you can use a test breakfast containing at least 120 grams of carbohydrates, 30 grams of which should be easily digestible (sugar, jam, jam).

FEATURES OF PREPARATION FOR INDIVIDUAL LABORATORY TESTS

Cholesterol research and lipid spectrum

To determine cholesterol and lipid spectrum, blood is taken strictly after a 12-14 hour fast. It is necessary to discontinue drugs that lower blood lipid levels within 2 weeks, unless the goal is to determine the lipid-lowering effect of therapy with these drugs. On the eve of blood collection, alcohol intake should be avoided: the presence of alcohol in blood is a common cause of hypertriglyceridemia, even in fasting patients. If a lipid test is performed in a patient who has had a myocardial infarction, blood should be taken either within 24 hours after the infarction or after 3 months, since lipid metabolism is impaired during the recovery period.

Uric acid

It is necessary to follow a diet in the days preceding the study - refuse to eat foods rich in purines: liver, kidneys, limit meat, fish, coffee, tea, alcohol in the diet as much as possible. Intense physical activity is contraindicated. It is necessary to discontinue medications such as caffeine, theobromine, theophylline, salicylates, ascorbic acid, antibiotics, sulfonamides, thiazole derivatives.

Cortisol

On the eve of the study, avoid taking medications such as glucocorticoids, estrogens, oral contraceptives. It is also necessary to avoid drinking alcohol, exercising, smoking, stressful situations. Blood sampling is carried out no later than 2 hours after sleep and before 10 am.

Prostate-specific antigen (PSA)

Blood sampling should be performed before palpation examination and massage of the prostate gland (PG), laser therapy, radiography, cystoscopy, colonoscopy. These therapeutic and diagnostic measures can cause a more or less pronounced and prolonged rise in PSA levels in the blood. Since the extent of such changes is unpredictable, blood sampling must be carried out either before or a week after the manipulations.

Diagnosis of infectious diseases (including urogenital infections)

Blood sampling for diagnostics is carried out before the start of taking antibacterial and chemotherapy drugs or no earlier than 10–14 days after their discontinuation. When performing tests for the presence of infections, it should be taken into account that depending on the period of infection and the condition immune system Any patient can have a false negative result. But, nevertheless, a negative result does not completely exclude the presence of infection and in doubtful cases it is necessary to re-test.

Immunogram

A blood test is taken strictly on an empty stomach, after a 12-hour fast and always before starting to take antibacterial, anti-inflammatory and hormonal drugs or no earlier than 2 weeks after their cancellation. If on the eve of the test there was a rise in temperature, any acute or exacerbation of a chronic disease, then it is better to reschedule the test.

Allergens

To exclude false negative results, it is necessary to refrain from taking anti-allergy medications 3 to 5 days before taking a blood test.

Prolactin

Blood is drawn in the morning, no earlier than 3 hours after waking up. Considering that prolactin levels can increase as a result of physical or emotional stress, after sexual intercourse, after staying in a sauna, or drinking alcohol, it is necessary to exclude these factors before the study.

Thyroid hormone test

2 - 3 days before the study, do not take iodine-containing drugs, 1 month - thyroid hormones (to get true basal levels), unless there are special instructions from the endocrinologist. However, if the purpose of the study is to control the dose of thyroid hormone drugs, blood is drawn while taking the usual dose.

Thyroglobulin

It is advisable to conduct the study at least 6 weeks after thyroidectomy or treatment. If such diagnostic procedures, like a biopsy or thyroid scan, then a study of the level of TG in the blood must be strictly carried out before the procedures.

Somatotropic hormone

3 days before taking blood, it is necessary to exclude sports training and stressful situations. 1 hour before blood collection - smoking. The study is carried out on an empty stomach (12 hours after the last meal). The patient should be completely at rest for 30 minutes before blood is drawn. Avoid stress during the blood collection process.

GENERAL URINE ANALYSIS

Failure to comply with the rules for collecting, timing and storage of samples obtained for research leads to a negative result!

Take tests constantly in the same laboratory - and your doctor will approximately know your personal normal values and any deviation from the norm will be immediately noticed by him.

Home " Analyzes » Clinical interpretation of laboratory results. Analysis decoding. Norm or pathology? Factors influencing laboratory results

Factors influencing test results. When is a blood test ordered? Factors influencing laboratory results

3.2. Factors influencing the quality of laboratory tests. Classification of factors

3.3. Sources of error in the preanalytical phase outside the laboratory

Biological and other factors

Standards for interpreting analyses. The concept of reference values ​​and reference interval.

Analysis decoding. Norm or pathology?

Reference ranges

Why may reference ranges vary between laboratories?

Factors influencing laboratory results

EATING

PHYSICAL EXERCISE

EMOTIONAL STRESS

GENDER OF THE PATIENT

PATIENT AGE

PREGNANCY

MENSTRUAL CYCLE

BIOLOGICAL RHYTHMS

TAKEN MEDICINES

SMOKING

DIAGNOSTIC AND TREATMENT MEASURES

SAMPLING FREQUENCY

POSITION OF THE PATIENT'S BODY WHEN TAKING BLOOD

PLACE AND TECHNIQUE FOR BLOOD COLLECTION

OTHER FACTORS

How to properly prepare for research in a clinical diagnostic laboratory

BLOOD TEST (CLINICAL, BIOCHEMICAL, IMMUNOENzyme)

GLUCOSE TOLERANCE TEST (SUGAR CURVE)

FEATURES OF PREPARATION FOR INDIVIDUAL LABORATORY TESTS

Cholesterol research and lipid spectrum

GENERAL URINE ANALYSIS

Standards for interpreting analyses. The concept of reference values and reference interval.