LABORATORY DIAGNOSIS

From Big Medical Encyclopedia

LABORATORY DIAGNOSIS (grech, diagnostikos capable to distinguish) — the section of clinical diagnosis studying methods of assessment physiological and recognitions and estimates of morbid conditions and diseases, based on researches of cellular and chemical composition, physical and chemical and biological properties of fabrics and liquids of an organism and also methods of detection of causative agents of diseases.

In sovr, medicine a lab. information occupies one of the leading places among objective diagnostic data. Reflecting metabolic and cellular processes, a lab. data allow to reveal the earliest aberrations, sometimes long before emergence of subjective feelings, a wedge, manifestations and visible structural changes of the struck bodies.

Scientific basis of L. is the medical scientific discipline called in the USSR clinical by L., abroad — clinical biology, clinical pathology, laboratory medicine. Its tasks include studying of patterns and establishment of limits of normal individual fluctuations of each studied parameter of structure biol, fabrics and liquids; studying of patterns of interrelation patol, deviations of these parameters with specific forms of pathology (a clinical pathobiology and a patobiokhimiya); development of methods of a research of chemical and cellular composition biol, liquids; development of requirements to quality of performance of analytical methods and means of ensuring of these requirements (clinical analytics); establishment of diagnostic value separate lab. tests and their combinations, development of optimum ways of their use in diagnosis of diseases (actually L.).

In a wedge, medicine methods L. apply hl. obr. for establishment of the diagnosis of a disease, for the characteristic of weight, the period and term of a disease, sometimes for definition of its forecast, and also for control of results of treatment.

History

Instructions on value of a research of urine at recognition of diseases, in particular a diabetes mellitus, contain in ancient sources Indian (see. Ayurveda ) and Chinese medicine. Ancient Egyptian priests resorted to a research of urine for diagnosis of pregnancy. Premises of creation scientific L. appeared in 15 — 16 centuries: in Gusancis and Paracelsus's works it was noted possible a wedge, value of weighing and a chemical blood analysis and urine. To development of L. were promoted by such events as the invention of a microscope and the colorimeter, discovery of cell structure, and also achievements of chemistry, biochemistry and a wedge, medicine. Founders of clinical chemistry it is considered to be the chemist R. R. Boyle who published article about the program of a research of human blood, and the doctor Langrish in 1684 (V. Langrish) printed results chemical and physical. blood test of patients with different types of fever. In 18 — 19 centuries a certain contribution to formation of bases a wedge, chemistry was brought by M. V. Lomonosov, A. Lavoisier, I. Bertselius. Gei-Lyussak, etc. R. Brayt, showed value of a research of urine for diagnosis of damages of kidneys. In 1821 W. Prout offered the elementary devices for carrying out a lab. researches at a bed of the patient at diabetes, defeats of urinary bodies, adjournment of stones in secretory bodies. L. came under influence of the ideas of J. Lister, L. Pasteur, R. Virkhov, G. Mendel, I. P. Pavlov.

The microscopy in medico-laboratory researches was applied in 30 — the 40th there are 19 century. In 1838 there were tables of microscopic precipitation patterns of urine, in 1844 to Donna (And. Donne) published a course of microscopy for medical researches, with" 1843 under J. F. Simon's edition one of the first magazines on a lab is issued. to researches one of the first guides to L is also the same year published. — J. J. Scherer's monograph «Chemical and microscopic examinations at pathology». In the 50th 19 century in practice of L. implemented colorimetry. Large contribution to development of L. in 19 — 20 centuries brought Wang - den - Berg (A. A. N., Van den Bergh), J. Kjeldahl, H. Burchard, Folin (O. Folin), I. Ch. Bang, D. D. Van Slyke, E. J. Conway, P. Astrup.

The first domestic publications on L. belong to 1843. In 1851 S. A. Smirnov's work «About uric acid», and one year later — the brochure of Uroskopiya is published. Since 1885 in St. Petersburg in-those improvements of doctors prof. M. I. Afanasyev gives a course a wedge, microscopy and bacteriology, and since 1895 A. V. Paul — a course of lectures on a lab. to researches.

Outstanding scientific contribution to development of various sections L. were brought by A. Ya. Danilevsky, M. V. Nentsky, A. V. Palladiya, A. Ya. Altgauzen, S. R. Mardashev, A. A. Pokrovsky, I. I. Ivanov, V. S. Ilyin, S.E. Severin, G.E. Vladimirov, V. N. Orekhovich, I. A. Kassirsky, and also authors of the domestic guides and monographs on a lab. to diagnosis (V. E. Predtechensky, E. A. Kost, etc.).

Contents and industry structure of laboratory diagnosis

Theoretical basis wedge. L. are fundamental sciences — chemistry and biology which progress along with use of achievements of physics and the equipment defines sovr, possibilities of L. According to objects and methods of researches, and also allocation of medical disciplines a wedge. L. creates the industries — a wedge, biochemistry, a wedge, a lab. toxicology, a wedge, immunology, a wedge, microbiology, a wedge, parasitology, a wedge, cytology, in a cut independent value have a wedge. lab. hematology and wedge, cytology of tumors. Industries wedge. L. develop to some extent independently and according to development basic for them theoretical (e.g., immunology, toxicology) and a wedge, disciplines. So, e.g., snowballing a wedge, immunology in 60 — the 70th 20 century was caused both by achievements of theoretical immunology, and increase in the practical importance immunol, problems in connection with development of techniques of organ and tissue transplantation, studying of autoimmune diseases, immunodeficiency. Despite relative independence of each of the industries a wedge. L., between them exist the close ties combining them in uniform complex scientific discipline on the basis of a community of research problems and unity of the studied environment and the most studied organism. Different types of researches combine within the diagnostic programs relating to certain types of pathology, the methods of a research developing in each of the industries are mutually used. So, chemical methods are used in immunology (immunochemistry), in cytology (cytochemistry), in microbiology (biochemical, methods of differentiation of microorganisms) etc. Immunol, methods entered a wedge, biochemistry, parasitology, microbiology, hematology. At the certain levels of rendering medical aid different types a lab. researches are carried out by the same workers, within uniform laboratory.

Opportunities modern L. are characterized by the nomenclature a lab. researches, i.e. quantity of types of researches and number of certain components (parameters) in the studied substrate, and also increase in their quality in connection with implementation of more exact or more specific methods that increases informational content a lab. data.

Philosophy of use of methods of laboratory diagnosis. Depending on a wedge, tasks lab. researches can be conducted once and repeatedly (in dynamics of overseeing by disease, napr, at crisis and in the mezhpristupny period, for studying of a day-night rhythm, for control of influence of treatment, during the carrying out funkts, or pharmakol, tests with loading or braking of the studied system), for the characteristic of one or many sides of cellular or chemical composition of bioliquids (so-called bulk analyses, comprehensive examination, a konstellyation a lab. tests).

Single-step multilateral lab. inspection can have or all-search character (at the first contact with patients, at receipt in a hospital, at routine maintenance), or to be purposeful (inspection of risk groups, a research for specification of the diagnosis). The method of differential and diagnostic programs which are aimed at differentiation within group of relatives on a wedge, to displays of diseases is very perspective.

The obligatory requirement to diagnostic a lab. to researches reliability of the received results is. The method cannot be recommended if assessment of its reliability or analytical suitability is not carried out. Reliability of a method is characterized by its specificity, sensitivity, and also correctness and reproducibility of results of a research.

Specificity of a method is characterized by an opportunity with its help of establishment only defined (intended for a research) properties of the studied substrate. Therefore at assessment of specificity character and extent of influence of other factors on results of a research of the defined property is specified.

Test-sensitivity is characterized by its opportunity to measure (to reveal) the studied property of substrate at the minimum quantities of the last. For methods of definition of concentration of substances it is defined by the smallest distinction between two concentration of the studied substance, a cut can be established by this method.

Correctness of results of researches is checked by compliance of an average value of results of measurements with the true size of the measured parameter. For methods of definition of chemical components of substrate correctness of measurements is determined, e.g., by way of additive in biol, liquid of precisely weighed amount of the studied substance with the subsequent its definition by this method or in the way of mixing in different ratios of tests of bioliquids with low and high concentration of substance, and also a reference way (comparison with the method having the correctness established earlier). Hit rate of results is estimated statistically.

Reproducibility of results of researches is characterized by extent of their coincidence at a repeated research of the same test biol, material. Reproducibility is expressed by size, the return to coefficient of variation of results (i.e. the attitude of a mean square deviation towards average arithmetic). The coefficient of variation is less, the reproducibility is higher. Considering a wedge, purpose of methods L., the errors determined by studying of opinions of experts-clinical physicians set also medical acceptance limits.

The correct diagnostic information with the help a lab. researches it is possible to receive, knowing specificity given a lab. the test for diagnosis of a certain type of pathology, and also normal amounts of results of researches, limits inside - and interindividual fluctuations and influence on them of medical and diagnostic procedures and means.

Truly normal (reference) amounts lab. indicators consider the sizes found at carefully inspected, selected group of healthy faces at the age of 20 — 30 years. In the groups of persons differing on any or to several signs (on a sex, age, a habital, a profession etc.), determine sizes a lab. indicators, normal for this contingent. At assessment of deviations of sizes lab. indicators in diagnostic process has value and knowledge of their individual sizes at this patient established earlier at preventive and dispensary inspections. Comparing found at inspected results a lab. researches with normal for it (established at a research in a healthy state) and for the contingent corresponding to it, and also with reference sizes, it is possible to receive the most reliable judgment of character of the found deviation.

At a wedge, assessment a lab. data it is necessary to consider that essential and quite often long impact on them is exerted carried out before a lab. a research of the procedure of diagnostic or to lay down. character (introduction of X-ray contrast weight or dye, injection of medicine, physiotherapeutic procedures, etc.). So, after administration of X-ray contrast mix it is impossible to receive adequate results of a research of iodic exchange; treatment dopegity, tetracycline, quinidine distorts results of a flyuorimetrichesky research of catecholamines etc. The majority modern to lay down. means the lab influences results. researches at the expense of pharmacological (in an organism) or technological (at a research of test) interferences. Violations of the rules of capture of material for a lab. researches (too long pulling of a shoulder a plait at capture of blood from a vein, excessively traumatic venipuncture), unfavorable conditions of its transportation in laboratory can also cause the wrong results of a research. Reliability of results depends on quality of the methods applied by laboratory, devices, reactants, calibration materials, on care of work of personnel. If deviation lab. indicators it is caused by pathology, at repeated researches tendentiousness of changes, i.e. repeatability of deviations, their orientation in most cases comes to light. Consensual changes several a lab are characteristic of some forms of pathology. indicators; e.g., at acute inflammatory processes quantity of leukocytes in blood, ROE, the maintenance of a number of enzymes, etc. at the same time can change.

Some laboratory tests are specific to disturbances of activity of certain bodies or for a certain type of pathology (e.g., organospetsifichesky isoenzymes, Paraproteina at a multiple myeloma); however the most part of tests yields results which have only probabilistic diagnostic character. So, e.g., acceleration of ROE is noted also at a bacterial inflammation, and at autoimmune process, and at a tumor. In assessment of suitability a lab. the test for diagnosis of a certain form of pathology use criteria of diagnostic specificity, sensitivity, efficiency a lab. the test and the applied method of a research. At the same time consider the frequency of both true, and false positive and false-negative results.

Diagnostic sensitivity of the test at a certain disease represents percentage expression of frequency of only truly positive takes of the test at patients with this disease. Diagnostic specificity of the test at a certain disease represents percentage expression of frequency of truly negative takes of the test at the persons who do not have this disease. The diagnostic importance of positive takes is expressed by percentage of truly positive takes to total number of positive takes, i.e. including as well false positive. The diagnostic importance of negative takes is expressed by percentage of truly negative takes to total number of negative takes. Diagnostic efficiency of the test is expressed by percentage true (both positive, and negative) test results to total number of the received results. In calculations of the listed characteristics a lab. the test allowance for the frequency of a disease of this disease among total number of inspected is entered.

Quality control of laboratory researches. For identification and assessment of systematic and accidental errors of results of the measurements performed in laboratory exercise intra laboratory and interlaboratory control of quality a lab. researches. At the same time use a number of criteria of quality: 1) accuracy of measurements, i.e. proximity of their results to a true value of the measured size; high precision of measurements corresponds to small errors of both systematic, and accidental measurements; 2) convergence of results of measurements, i.e. lack of essential distinctions between them at the measurements which are carried out in identical conditions; 3) reproducibility of results of measurements — lack of essential distinctions between them at the measurements which are carried out in different conditions (in various time, in different places); 4) correctness of measurements, i.e. lack of systematic errors in results.

Quality control lab. researches carry out by comparison of results of the measurements performed in laboratory with control and determination of size of a deviation. For control measurements use control materials: water solutions of standards, the merged blood serum prepared in the laboratory, biol, the material made in the production way both with investigated, and with the unexplored maintenance of components (serum, plasma, urine, cerebrospinal liquid, blood cells, etc.), materials of an artificial origin, specific control means (smears, mikrobiol, cultures, pathogenic fungi, suspensions of cysts, etc.). Main requirements to control materials: identity on physical. - to chemical properties to the analyzed sample; stability at long-term storage; the minimum variability of structure and properties in a series; suitability for identification of systematic and accidental errors. Control of convergence and reproducibility of results of researches is carried out by means of control material with unexplored contents; for control of correctness only material with the studied maintenance of components is used.

Intra laboratory control includes control of convergence, reproducibility and correctness of measurements. Reproducibility is considered sufficient if the size of coefficient of variation of results for researches of substrates does not exceed 5%, and for definitions of activity of enzymes of 10% that corresponds to percentage expression of the relation about 1/8 limits of normal fluctuations of the studied parameters to the average size of norm. For assessment of reproducibility of results it is convenient to use control maps on which mark daily results of control researches. For map development previously within 20 days investigate control material of one series of release and results daily register. From the received 20 results calculate the average size and coefficient of variation. If coefficient of variation is more than admissible, check all course of the analysis, remove the causes of unsatisfactory reproducibility and repeat a preliminary stage. The control card is built for each controlled indicator and only for this series of control material. Results of a daily research of checks of the same series in the next days plot in the form of a point and use a lab for assessment of reproducibility. researches.

Control of correctness of results of measurements is carried out on condition of their good convergence. Can be control methods comparison of results of own definitions with rated value of control materials; comparison of results with results of a reference method; participation in an interlaboratory experiment on quality control; the additional research of test of material, to a cut is previously added exact amount of pure substance; researches of tests with various concentration. The received results process statistically. In addition to a method of checks use a method of accumulation of the sums, the principle to-rogo is that daily calculate a difference between the average size of the received results and rated value and put with a difference of previous day. The algebraic sum of positive and negative deviations of results from their expected size is plotted. The correct results fluctuate near the line of a constant deviation. In the absence of control material use the method offered by Wade (M. of E. Waid) and R. G. Hoffman who is based on a statistical analysis of results of researches of tests of patients. Test-sensitivity depends on change of the contingent of the hospitalized patients, on working conditions and on a time factor.

Interlaboratory control is a comparative quality control of results of the researches received in a number of laboratories during the use of uniform control material. It includes control of reproducibility and correctness and once a quarter, under the methodical leaders of the control centers created on the basis of republican, regional and regional BCs is carried out at least. The control centers define the purposes, tasks and a procedure of check experiment, collect and study results of control definitions and develop recommendations about improvement of quality of work of laboratories.



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V. V. Menshikov, E. H. Garanina.

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