QUALITY CONTROL
Internal quality control system:
There are three stages:
Organization and quality assurance of the preanalytical stage of laboratory research.
The basis of quality assurance at the pre-analytical stage is the development and strict adherence to the instructions for the quality of conducting this stage of laboratory research, as well as the maximum standardization of all the main points.
The complexity of the organization of the preanalytical stage in the clinical diagnostic laboratory is largely due to the fact that manual labor prevails here and the fact that the numerous personnel who serve the patient at this stage have different subordinates and different levels and content of education. If orderlies, nurses, doctors, procedural nurses, couriers work outside the laboratory, then registrars, laboratory assistants, technologists, doctors of clinical laboratory diagnostics serve this stage inside the laboratory.
The non-laboratory part of the pre-analytical stage begins with the appointment by the doctor of a specific patient of a certain group of analyzes (component or characteristic of the sample to be measured) included in the laboratory study. It is he who forms the application with the list of analytes he needs, determines the conditions of patient preparation (for example, fasting, the time of taking or collecting biological material), the material to be examined (blood, urine, feces, semen, etc.).
Preparing the patient for research is one of the important components of the non-laboratory part of the stage. The doctor must explain to the patient the need for laboratory tests and inform the patient about how he needs to prepare for the tests.
When contacting us, patients are informed of the conditions for proper preparation before passing the analysis. On the website mtsclinic.ua, a special section contains recommendations for preparing for the analysis. But your doctor's training recommendations are paramount!
Qualitative sampling of the material is one of the standardizing and determining points of all laboratory research.
Vacuette vacuum systems (Greiner Bio-One, Austria) are used to collect biomaterial. The use of vacuum systems is a necessary step in creating standard conditions for taking, transporting and storing biological samples from patients. The implementation of such systems affects all stages of laboratory research and, in general, brings the organization of laboratory work to another level. Over 95% of blood samples in the US and Western Europe are collected using vacuum systems.
Of particular importance is the standardization of the process of transporting samples to the laboratory. General rule: deliver the material to the laboratory as soon as possible. During transportation, the required temperature regime is observed, transportation of biomaterial is carried out in special refrigerator bags.
The stability of individual analytes depending on time, temperature, exposure to direct light.
The laboratory part of the pre-analytical stage begins with the delivery of the sample and application to the laboratory. Upon receipt of the material, the registrars check the compliance of the samples with the directions, the condition of the samples, the time that has passed since they were taken, and note the time of the sample's arrival in the laboratory.
The criteria for refusing to accept the material for research are clearly defined: discrepancy between the data of the application and the label on the test tube (initials, date, time of taking the material, etc.); lack of a label on a test tube or other container, inability to read the application and/or label (patient data, signature of the procedure nurse); material taken or collected with the wrong anticoagulant or preservative; exceeding delivery terms; the presence of clots in whole blood with an anticoagulant, etc. After centrifugation, the most frequent failure criteria are hemolysis, ictericity, and lipemia of the sample, depending on the method of measuring the analyte. For the material to be centrifuged, there is a certain standard protocol that defines the mode of centrifugation.
Organization and quality assurance at the analytical stage
Unlike the pre- and post-analytical stages, where the main forms of control are periodic inspections (external and internal), the quality control of the analytical stage is, first of all, an assessment of the results of measurements of control samples.
As a result of any measurement, there is always an error or error - a deviation of the measurement result from the true value of the measured quantity. Even the best analytical methods for determining the concentration of a substance in a sample do not give the same result: with repeated measurements of the same substance, in the same sample, with the same method, there is always a certain scatter of results. Any measurement procedure performed in the laboratory includes a number of steps - preparation of samples and reagents, dosing, incubation, measurement of optical density, etc., and at each of them some error occurs that affects the final result. The result of the measurement, thus, contains the contributions of all these errors.
When using statistical methods in quality control, measurements are based on the assumption that the frequency distribution of the results of multiple measurements of the same analyte in the same control material by the same analytical method has the form of a normal or Gaussian distribution. The similarity of measurement results is the closeness to each other of the results of measurements of the same quantity performed in one analytical series.
Another term is used: intra-batch reproducibility. A numerical measure of reproducibility and convergence is the root mean square deviation (S) and coefficient of variation (СV).
Internal laboratory quality control and external assessment of research quality are distinguished.
Intra-laboratory quality control means checking the results of measurements of each analyte in each analytical series, which is carried out daily directly in the laboratory by using accepted algorithms for evaluating the measurements of control materials, mainly with the aim of evaluating their reproducibility (the closeness of the results of measurements of the same value obtained in intra-laboratory control - detection and elimination of unacceptable deviations from the stable performance of the test in the laboratory,
i.e. detection and elimination of unacceptable analytical errors.
Control material is a homogeneous, stable material, the results of which are used to estimate the error of analytical measurements performed. One of the main principles of choosing a control material is that when using reagents and calibrators of one manufacturer, it is recommended to use certified control materials of another manufacturer. In the Independent Laboratory, in the vast majority of tests in accordance with this requirement, control materials from the company Bio-Rad (USA) are used, at least in two levels of analyte concentration. Bio-Rad is one of the world's oldest and largest manufacturers of control materials for biochemical, immunochemical, hematological and some special studies.
Control charts (Levey-Jennings charts) are used for systematic operational monitoring of the stability of the analytical system based on the results of the study of control samples. The control chart is a graphical representation of the statistical characteristics of variations of the analytical system obtained in the reference series, which meet the requirements for its accuracy. It is used for systematic operational monitoring of the stability of the analytical system based on the results of the control samples that are plotted on the map. The control chart, built on the basis of a series of measurements, is a graph, on the abscissa axis of which the number of the analytical series (or the date of its execution) is placed, and on the ordinate axis - the value of the indicator determined in the control material. A line is drawn parallel to the abscissa axis corresponding to the average arithmetic value Xср and the lines corresponding to the control limits calculated based on the value of the root mean square deviation are marked.
Construction of control cards with subsequent archiving of intra-laboratory quality control data is carried out automatically within the laboratory information system. Operational quality control of analyte measurement results in patient samples is carried out by measuring this analyte in the control materials of each analytical series and plotting the obtained results on control charts.
The purpose of internal laboratory quality control is to identify and eliminate deviations from the stable performance of the test in the laboratory. Control charts are built for each analyte and each level of control material intended for operational quality control.
The purpose of the external evaluation of research quality is to evaluate the compliance of research results with established norms of analytical accuracy. External quality assessment is an objective verification of the results of the laboratory, carried out periodically by an external organization. Any well-organized system of external quality assessment is designed to compare the results of analyzes between laboratories with the aim of harmonizing the results of laboratory studies.
In a specific clinical diagnostic laboratory, an optimal system of external quality assessment, which provides adequate information about the correctness of the measurement of most or all analytes, can be created only by regularly and simultaneously participating in several systems of external quality assessment. This especially applies to large laboratories with a wide list of analytes and modern analytical systems used for their measurement.
Creation of analytical quality is a set of measures to implement requirements for analytical quality:
. choice of analytical method;
. choice of analytical systems;
. selection of reagents;
. validation of the method and reference values;
. compliance with technology (calibration, maintenance of the analyzer);
. personnel training, etc.
Organization and quality assurance at the post-analytical stage
Like the preanalytical stage, this stage can be divided into in-laboratory and out-of-laboratory parts.
The main element of the intra-laboratory part of the post-analytical stage is the verification by a qualified laboratory specialist of the result of the analysis for its analytical reliability, biological probability or plausibility, as well as the comparison of each result with reference intervals.
At the stage of checking the research results, it is important to take into account the factors that prevent the determination of the analyte (such as hemolysis, lipemia, excessive jaundice, paraproteinemia, etc.) and rejection criteria. The degree of influence of these factors often depends on the method of measuring the analyte, therefore, at the pre-analytical stage, a questionable sample can be accepted for research. In this case, during the final verification of the results, the analytes, the measurements of which could be affected by these factors, are highlighted in the report form.
Special attention is paid to the formatting of the report forms: the grouping of the results according to the pathophysiological principle with reference values is used, which greatly simplifies the interpretation of the results. The form is made in such a way that the clinician, looking at it, receives the most important information, without being distracted by the number of zeros after the comma, ones, as well as irrelevant reference intervals (age, gender). This part of the stage ends with the signature (authorization) of the report form, i.e. the formation of the final product of the laboratory process and its transfer to the clinician.
There are several ways to get results:
-
by phone (CODE WORD)
-
by e-mail (upon prior application);
-
in the medical center
-
at any of the blood collection points
-
delivery by courier (paid additionally);
In our medical center, you can always consult with doctors based on the results of research.
As for the pre-analytical stage, the main form of quality control of the post-analytical stage is periodic external and internal inspections (audits).
Conclusion
The existing idea of ensuring the quality of the results of laboratory research as the qualitative performance of only the analytical stage is very narrow and cannot be considered a full-fledged and sufficient basis for ensuring the guaranteed quality of the work of specialists in clinical laboratory diagnostics. Their work can be fruitless in the event of an incorrectly completed application for research, in violation of the rules of blood collection, mistakes made during the transportation of biomaterial to the laboratory. Just as late delivery of a laboratory report to the physician or failure to use the information received by the clinician devalues all previous efforts to ensure the quality of the actual measurement.
External quality control system:
Interlaboratory quality control of laboratory research is a control of the comparability of results obtained in several laboratories on the same control material using the same methods or methods that give statistically reliable matching results.
As a rule, at least 20 laboratories participate in interlaboratory quality control of laboratory research.
Implementation of interlaboratory quality control makes it possible to solve the following tasks:
. compare the quality of work of all laboratories participating in the control;
. identify systematic, random and gross errors in the results of control determinations;
. evaluate the quality of used research methods, equipment, reagents, etc.
In addition, each laboratory can compare the quality of its work with the results of other laboratories that participated in the control. In interlaboratory quality control, the best results are achieved by those laboratories that have established intralaboratory control.