Biological variation
The results of laboratory studies are subject to the influence of biological and analytical variation. If the analytical variation depends on the conditions of the test, the magnitude of the biological variation is from a whole set of factors. The general biological variation of the studied indicators is due to the intra-individual variation observed in the same person as a result of the influence of biological rhythms( different times of the day, year) and interindividual variation caused by both endogenous and exogenous factors, the main of which are presented in Fig.
Biological factors( physiological factors, environmental factors, sampling conditions, toxic and therapeutic factors) can influence the results of laboratory studies. Some of them can cause real deviations of laboratory results from reference values outside of the connection with the pathological process [Menshikov VV, 1995].These factors include the following.
■ Physiological patterns( influence of race, gender, age, type of constitution, nature and amount of habitual activity, nutrition).
■ Influence of the environment( climate, geomagnetic factors, time of year and day, composition of water and soil in the habitat, social and household environment).
Fig. Sequence of evaluation of the results of laboratory studies
Fig. Sequence of evaluation of laboratory results
■ Impact of occupational and household toxic agents [alcohol, nicotine, drugs) and iatrogenic effects( diagnostic and treatment procedures, medicines( AS)]
■ Sample collection conditions( meal intake, exercise, body position, stress during sampling, etc.)
■ Blood sampling technique( method of taking, tools and utensils, preservatives, etc.)
■ Incorrect( in time) material intake
■ Conditions( temperature, shaking,influence of light) and the time of transportation of the biomaterial for research into the laboratory
Figure Factors influencing the biological variation [Garanina EN, 1997]
Figures influencing the biological variation [Garanina EN, 1997].
Consider the effect of the most important factors on the results of laboratory tests:
Food intake: The diet, the composition of the food taken, and the breaks in its administration have a significant effect on a number of laboratory indicators. After 48 hours of fasting, the concentration of bilirubin in the blood can increase. Fasting for 72 hours reduces the blood glucose concentration in healthy people to 2.5 mmol / L( 45 mg%), increases the
concentration of triglycerides( TG), free fatty acids without significant changes in cholesterol concentration( CS) [Statland BE et al., 1973].
The use of fatty foods can increase the concentration of potassium, TG and alkaline phosphatase. The activity of alkaline phosphatase in such cases can be especially increased in people with the O or B blood group [Remes K. et al., 1994].Physiological changes after eating fatty foods in the form of hyperchylomicronemia can increase the turbidity of blood serum( plasma) and thereby influence the results of measuring the optical density. The increase in serum lipid concentration can be after the patient has consumed butter, cream or cheese, which will lead to false results and will require re-analysis.
Consuming a large amount of meat, that is, foods high in protein, can increase the concentration of urea and ammonia in the serum, urate in the urine. Food with a high ratio of unsaturated fatty acids to saturated can cause a decrease in serum cholesterol concentration, and food rich in purines causes an increase in urate concentration. Bananas, pineapples, tomatoes, avocados are rich in serotonin. When they are used 3 days before urine is tested for 5-hydroxyindole acetic 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 adrenals. The intake of alcohol increases the concentration of lactate, uric acid and TG in the blood.
The general rule for excluding the influence of food intake on the results of laboratory tests is the collection of blood after a 12-hour fasting.
Exercise. Physical load can have both a transient and a long-term effect 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 of 180% in the concentration of ammonia and 300% in lactate, an increase in the activity of creatine kinase( CC), aspartate aminotransferase( AST), lactate dehydrogenase( LDH) [Garza D., Becan-McBride K., 1989].Physical exercises activate blood clotting, fibrinolysis and functional activity of platelets. Changes in these indicators are associated with the activation of metabolism, they usually return to their original( before physical load) values soon after the physical activity ceases. Nevertheless, the activity of certain enzymes( aldolase, CC, AST, LDH) may remain elevated within 24 hours after 1 hour of intense physical activity. Prolonged physical activity increases the concentration of sex hormones in the blood, including testosterone, andros-tendeon and luteinizing hormone( LH) [Henry J. B, 1996].
Emotional stress can cause transient leukocytosis, a decrease in iron concentration and a change in the level of catecholamines in the blood. Severe anxiety, accompanied by hyperventilation, causes an imbalance in the acid-base state( CBS) with an increase in the concentration of lactate and fatty acids in the blood.
Other factors. Among other factors influencing the results of studies, the daily rhythms of homeostasis, age, sex, pregnancy, geographical location of the terrain, height above sea level, ambient temperature, smoking are important. In smokers,
can increase the concentration of carboxyhemoglobin( HbCO), catecholamines in blood plasma and cortisol in serum. Changes in the concentration 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 the concentration of hemoglobin( Hb), the number of erythrocytes, the average volume of erythrocyte( MCV) and a decrease in the number of leukocytes. In connection with this, it is recommended that laboratories establish their own local reference values for their population.
In order to reduce the effect of the factors on the results of the tests, before taking blood for the study, abstinence from exercise and alcohol intake, changes in diet for 24 hours should be avoided. The patient should not eat after dinner, he needs to go to bed the day before in usual forhis time and get up no later than 1 hour before taking blood [Alstorm T. et al., 1993].It is recommended to collect blood from the patient in the early morning hours after a 12-hour night fast( baseline), which allows maximum standardization of the study conditions.
Medicinal products. Some drugs can have a significant impact on research results. For example, the reception of acetylsalicylic acid in determining the time of bleeding Duke should be canceled 7-10 days before the study, otherwise you can get a pathological result. In the event that the drug taken by the patient can affect the result of the analysis, and if it is impossible to cancel it, you should inform the laboratory about it.
The effect of drugs on the results of laboratory studies 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 index) due to the chemical and physical properties of drugs( interference).
Physiological effects of drugs and their metabolites are largely known to practitioners. Consider the value of interference, that is, interference of an extraneous factor in the results of the analysis.
Interference can be caused by the presence in the sample of the biomaterial of both endogenous and exogenous substances. The main endogenous interfering factors include the following.
■ Hemolysis, that is, the destruction of erythrocytes 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 determination of the concentration / activity of blood components such as bilirubin, lipase,, potassium, magnesium, etc.
■ Lipemia, which distorts the results of a number of colorimetric and nephelometric methods of investigation( especially in the study of phosphorus, total bilirubin, uric acid, total protein, electrolytes).
■ Paraproteinemia, which causes changes in the results of determination of phosphate, urea, kk, LDH, amylase by some methods.
The most frequent exogenous interfering factors are drugs or their metabolites. Thus, in the determination of catecholamines by the fluorimetric method in urine, the patient's accepted tetracycline may cause intense fluorescence;the metabolite of propranolol 4-hydroxypropranolol interferes with the determination of bilirubin by the methods of Jendrassic-Gro-fa and Evelyn-Mello.
To identify the interference of drugs - one of the tasks of a doctor of clinical laboratory diagnostics. An important step in solving this problem is contacting the clinician to find out the nature of the medications taken by the patient.
The position of the body with blood sampling also affects a range of records. Thus, changing the patient's position lying on a sitting or standing position results in hydrostatic penetration of water and filtering substances from the intravascular space into the interstitial space. Substances having a large molecular weight( proteins) and blood cells with associated substances do not pass into the tissue, so their concentration in the blood rises( 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 sampling may also have a significant effect on laboratory test results( for example, the application of a tourniquet for a period of more than 2 minutes in blood collection from a vein can lead to hemoconcentration and an increase in blood protein concentration, coagulation factors, cell content).The best place of blood sampling for tests 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 currently used hematological analyzers, through which general clinical blood tests are carried out( cell counting, determination of Hb, Ht, etc.) are designed to work with venous blood, and in most countries in the countries where they are produced,they are certified and standardized to work only with venous blood. The calibration and control materials produced by the companies are also designed for the calibration of blood analyzer for venous blood. In addition, the collection of blood from the finger can be a number of methodological features that are difficult to standardize( cold, cyanotic, edematous fingers, the need for dilution of the blood being studied, etc.), which leads to significant variations in the results obtained and, as a consequence, toThe need for repeated studies to clarify the result. For general clinical examination, finger blood is recommended to be taken in the following cases.
■ For burns that occupy a large area of the patient's body.
■ If the patient has very small veins or little access to them.
■ With severe obesity of the patient.
■ With a susceptibility to venous thrombosis.
■ In newborns.
Puncture of the artery for blood sampling is rarely used( mainly for studying the gas composition of arterial blood).
The timing and conditions for the transport of biological material samples also play an important role in ensuring the quality of laboratory test results. When delivering material to the laboratory, it is always necessary to remember the features of some samples. For example, when taking arterial blood to examine a gas composition, the blood reservoir should be well clogged, immersed in ice water and delivered to the laboratory as soon as possible, as glycolysis in red blood cells and leukocytes causes a decrease in pH if the sample is about 20 minutes at room temperature. These requirements must also be observed in the study of capillary blood, which is taken to the heparinized capillaries. Blood for adrenocorticotropic hormone( ACTH), angiotensin I, II, renin also should be placed immediately after the fence in the ice and delivered to the laboratory as soon as possible.
In general, in order to avoid the influence of the time factor on the results of the analyzes, the delivery of the material to the laboratory must be made as quickly as possible. The earlier the serum is separated from red blood cells, the less influence of glycolysis( hence, the effect on the concentration of glucose, phosphorus and the activity of certain enzymes will be less).The concentration of bilirubin in the blood decreases under the influence of light( especially bright sunlight).The effect of light also increases the activity of alkaline phosphatase. The time factor is also very important for bacteriological studies( some bacteria die at room temperature).
The time for delivery of the biomaterial to the laboratory should fit into the intervals presented in the table. If they are observed, it is possible to minimize the negative effect of the time factor on the results of laboratory tests.
Table 1-1.Delivery times to the laboratory [Garza D., Becan-McBride K., 1989]
Table 1-1.Delivery times to the laboratory [Garza D., Becan-McBride K., 1989]
The specified time limits for delivery should be known to every clinician. If they are violated, repeated sampling is necessary, since it is not possible to exclude the influence of the time factor on deviations in the results of the studies.
In addition to all of the above, the amount of biological variation depends on the physiological function performed in the body by the analyte. The smallest biological variation is characteristic for substances most important for the stability of the composition and volume of extracellular fluids and blood( sodium, chlorides, calcium, magnesium, albumin, total protein, carbon dioxide).Variation of the average degree is characteristic for substances involved in the processes of anabolism( glucose, cholesterol, phosphorus).The components of serum, which are the final products of catabolism( uric acid, urea, creatinine), as well as substances and enzymes [LDH, AST, alanine aminotransferase( ALT), etc.), possess the greatest biological variation.