In connection with the improvement of the technological equipment of medical laboratories and the automation of many biomaterial analysis processes, the role of the subjective factor in obtaining the result has significantly decreased. However, the quality of the collection, transportation and storage of material still depends on the accuracy of compliance with the methods. Errors at the preanalytical stage greatly distort the results of laboratory diagnostics. Therefore, quality control of its conduct is the most important task of modern medicine.
The main stages of laboratory diagnostics
In laboratory diagnostics, 3 main stages are distinguished:
- preanalytical - the period preceding the direct study of the sample;
- analytical - laboratory analysis of biomaterial in accordance with the purpose;
- postanalytical - assessment and systematization of the data.
The first and third stages have two phases - laboratory and off-laboratory, while the second part of the diagnosis is carried out only inside the laboratory.
The preanalytical stage combines all the processes that precede the entry of a biological sample of CDL into the study. This group includes medical prescribing, preparation of the patient for analysis, and sampling of biomaterial with its subsequent labeling and transportation to a clinical laboratory. Between the registration of the sample and its sending for analysis, a short-term storage period passes, the conditions of which must be strictly observed to obtain an accurate result.
The analytical stage is a set of manipulations carried out with samples of biomaterial for their research and determination of parameters in accordance with the type of analysis assigned.
The postanalytical stage combines 2 stages:
- systematic assessment and verification of the reliability of the results (laboratory phase);
- processing by the clinician of the information received (extra-laboratory phase).
The clinician correlates the results of the analysis with the data of other studies, anamnesis and personal observations, after which he makes a conclusion about the physiological state of the patient's body.
Characterization and significance of the pre-laboratory stage in clinical diagnosis
As already noted above, the preanalytical stage of clinical laboratory diagnostics includes two phases:
- Non-laboratory - combines activities until biomaterial enters the CDL, including the purpose of analysis, sampling and labeling of samples, their storage and transportation to the study.
- Intralaboratory - is carried out within the framework of the CDL and includes a number of manipulations for the processing, identification and preparation of biomaterial for research. This also includes the distribution of labeled samples and their relationship to specific patients.
The laboratory part of the preanalytical stage takes 37.1% of the entire study time, which is even more than at the analytical stage. The extra-laboratory phase accounts for 20.2%.
In the preanalytical stage of laboratory research, the following main stages are distinguished:
- receiving a patient from a doctor and prescribing tests;
- execution of documentation required for analysis (application form);
- instructing the patient about the nature of the preparation for the analysis and the characteristics of the delivery of the material;
- biomaterial sampling (sampling);
- transportation to KDL;
- submission of samples to the laboratory;
- registration of samples;
- analytical and identification processing of material;
- preparation of samples for the appropriate type of analysis.
The combination of these manipulations takes 60% of the time of the entire diagnostic study. At the same time, errors may occur at each stage, leading to a critical distortion of the data obtained during the analytical stage. As a result, the patient may be diagnosed incorrectly or given an incorrect prescription.
According to statistics, from 46 to 70% of errors in the results of analyzes are attributed to the preanalytical stage of laboratory research, which, no doubt, is due to the predominance of manual labor in the process of its implementation.
Clinical trial variability
The results of the analytical stage of diagnosis alone cannot be objective, since they strongly depend on many factors - from the most basic (gender, age) to the conditions for each mini-stage that precedes the sample getting into the study. Without taking into account all these factors, it is impossible to assess the true state of the patient's body.
The variability of laboratory data under the influence of a number of external and internal conditions that accompany their receipt, as well as the physiological characteristics of the patient, is called intraindividual variation.
The final results of laboratory diagnostics are affected by:
- the conditions in which the patient was before taking the material;
- methods and conditions for taking analysis;
- primary processing and transportation of samples.
All these parameters are called factors of the preanalytical stage of laboratory research. The latter can be changed, in contrast to unremovable characteristics (gender, age, ethnicity, pregnancy, etc.).
The main groups of factors of the preanalytic stage of clinical laboratory research| Patient preparation | - Variations of the biological state of the body.
- The impact of external environmental conditions.
- The position of the patient’s body.
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| Biomaterial fence | A set of factors depends on the type of biomaterial. |
| Transportation | - Duration
- Type of sample container.
- Lighting.
- Mechanical stress (e.g. vibration).
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| Sample preparation | The correctness of the implementation of measures to maintain the stability of analytes or additional procedures that prepare the sample for analysis (for blood - centrifugation, aliquotation and separation from the sediment) |
| Storage | - Temperature.
- Lighting (for some samples).
- Freezing / thawing (for blood).
|
In most cases, when evaluating the results, the clinician does not take into account the influence of preanalytical factors and possible errors made at this stage. Therefore, it is so important that all stages of laboratory research are strictly subordinate to the standard.
Such regulation is contained in the corresponding GOST of the preanalytical stage, as well as in numerous methodological recommendations and instructions for medical staff, developed taking into account scientific data and the specifics of a particular institution. Proper qualified organization of the diagnostic process improves the quality of research and minimizes the likelihood of errors.
The main mistakes of the first stage of laboratory diagnostics
There are 4 groups of violations at the preanalytical stage:
- errors in the process of preparing for the capture of material;
- associated with direct sampling;
- processing errors;
- transportation and storage errors.
The first group of violations include:
- incorrect preparation of the patient;
- pass the test;
- incorrect labeling of containers for collecting biomaterial;
- improper selection of the additive necessary to stabilize the obtained sample (for example, an anticoagulant);
Violations in the preparation process can be caused by both the incompetence of the medical staff and the negligence of the patient himself.
The rules for conducting the pre-analytic phase are aimed at preventing most errors. In addition, they bring the diagnostic conditions to a single scheme, which makes it possible to objectively compare the results of studies with each other and with reference intervals (groups of values ​​of certain indicators that correspond to the norm).
The organized organization of the preanalytical stage of laboratory research according to the established scheme is called standardization. The latter can be both general and private in nature, taking into account the specifics of the work and technical equipment of a particular medical institution.
Standardization
In order to minimize the intraindividual variation of laboratory results, the organization of the preanalytical stage should be streamlined and subject to certain standards.
The standardization of the laboratory stage includes:
- rules for the appointment of tests (intended for the attending physician);
- main aspects of preparing the patient for the study;
- instructions for taking biomaterial;
- rules for sample preparation, storage and transportation of clinical material to the laboratory;
- sample identification.
In view of the wide specificity of various medical institutions and CDLs, there is no single standard that regulates their activities in detail. For this reason, common documents have been developed (international and domestic) containing universal requirements for the organization of the preanalytical stage of laboratory research. These rules are taken into account when drawing up individual standards at the level of specific medical organizations.
What is quality control?
As applied to medical diagnostics, the term “quality” means the reliability of the results obtained, which implies the maximum possible exclusion of the influence of variable factors of intraindividual variability and errors of medical staff.
The quality control of laboratory research is a set of measures aimed at confirming the compliance of the actual data of diagnostic information with objective values ​​necessary for a correct assessment of the patient's condition. In a narrower sense, this means checking each stage for compliance with the requirements of the standard. Quality control of the pre-laboratory stage implies the establishment of compliance of each stage of the process with GOST of the pre-analytical stage and other documents developed at a private level.
The presence of standards plays a huge role in minimizing diagnostic errors, but still can not exclude the subjective factor. At present, monitoring compliance with the rules of the preanalytical stage of laboratory research is a problem, since periodic external and internal checks can hardly be called effective.
Nevertheless, the approximation of process technology to a single system and the introduction of more convenient methods for working with biomaterial for staff can be a way out of this situation. One of these innovations was the use of vacuum tubes for collecting blood, which came to replace the syringe.
In the list of state medical standards, there are 2 main documents aimed at ensuring the quality of the pre-analytical stage:
- GOST 53079 2 2008 (Part 2) - contains guidance on the quality management of the entire laboratory diagnostic process.
- GOST 53079 4 2008 (part 4) - governs directly the preanalytical stage.
One of the key aspects of quality control is the coordination between groups of personnel involved in different stages of laboratory diagnostics.
GOST 5353079 4 2008 - ensuring the quality of the pre-analytical stage
This standard was developed on the basis of two Moscow medical academies and legally approved in December 2008. The document is intended for use by all types of enterprises (both private and public) related to the provision of medical care.
This GOST contains the basic rules of the preanalytical stage of laboratory research, designed to exclude or limit the factors of diagnostic variability that impede the correct reflection of the physiological and biochemical state of the patient's body.
The regulation of the standard includes:
- a description of the conditions that must be met by the patient in preparation for the analysis (contained in Appendix A);
- terms and conditions for taking biomaterial;
- requirements for primary processing of samples;
- rules for the storage and transportation of biological material in KDL (clinical diagnostic laboratories).
Requirements for handling biomaterial necessarily include safety measures for working with potentially pathogenic samples.
GOST of the preanalytical stage of laboratory research involves a detailed briefing of the staff of the medical institution and informing patients about the rules for preparing and conducting analyzes. According to the document, the process of taking and labeling the material should be clearly organized, and the laboratories are equipped with all the necessary equipment for sampling, storage and transportation of samples.
The content of GOST of the preanalytical stage of laboratory research is based on generalized scientific data on the influence of physical, chemical and biological factors on the state of cellular and material contents of materials taken from a patient.
Information on the stability of the components of the biomaterial is in Appendices B, C, and D, and data on the effect of drugs taken on the eve of the analysis on the results of studies is in Appendix D.
The rules of the preanalytical stage of clinical laboratory studies specified in GOST are of the nature of universal generalizing recommendations and are not a full-fledged methodological recommendation for the implementation of procedures related to analyzes. A full-fledged instruction is a combination of medical knowledge and skills that are consistent with the standard and features of the organization of the diagnostic process of a medical institution.
Requirements for taking biomaterial
A portion of any biomaterial taken for analysis is called a sample or sample, the sampling of which is carried out according to the instructions in order to determine the characteristics of the inspected lot (patient).
For each type of analysis, the GOST specifies its recommendations, however, they are generalized and do not include a detailed description of the technology of sampling the material, which must be clearly followed by the medical professional. However, the document lists personnel qualification requirements that imply a good knowledge of the methodology.
Features of blood sampling
For obvious reasons, blood is the main material for most laboratory tests. The fence can be carried out for research:
- blood itself;
- serum;
- plasma.
To analyze the components of whole blood, most often the material is taken from a vein. This method is ideal if it is necessary to determine hematological and biochemical parameters, hormone content, serological and immunological characteristics. If necessary, examine the plasma or serum, the separation of the desired fractions is carried out no later than one and a half hours after blood collection.
For a general analysis, blood is mainly taken from the finger (capillary). This option is also shown with:
- burn damage to most of the patient's body;
- inaccessibility or too small diameter of veins;
- high degree of obesity;
- identified predisposition to venous thrombosis.
In newborns, it is also shown to take material from the finger.
The material is taken from a vein using vacuum tubes. During this procedure, particular attention is paid to the duration of the application of the tourniquet (should not exceed two minutes).
Requirements for blood sampling at the preanalytical stage depend on:
- type of assigned research (biochemical, hematological, microbiological, hormonal, etc.);
- type of blood (arterial, venous or capillary);
- type of test sample (plasma, serum, whole blood).
These parameters determine the capacity and material of the test tubes used, the volume of blood required and the presence of additives (anticoagulants, inhibitors, EDTA, citrate, etc.).
Cerebrospinal fluid
According to GOST preanalytical stage, this procedure should be carried out in strict accordance with the established procedure. Sampling is recommended to be carried out shortly after sampling material for the study of blood serum, the results of which are usually compared with data on cerebrospinal fluid (CSF).
According to the instructions, the first 0.5 ml of the collected biomaterial must be removed, as well as CSF mixed with blood. Recommended sample volumes for adults and children are prescribed in section 3.2.2 of the GOST of the preanalytical stage of laboratory studies.
The CSF sample includes three fractions, which have the following names:
- microbiology;
- cytology (tumor cells);
- supernatant for clinical chemistry.
The total amount of material taken in adults should be 12 ml, and in children - 2 ml. 2 :
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This study is carried out in the morning and strictly on an empty stomach (at least 8 hours should pass between the last meal and delivery of the material). Alcohol is forbidden to drink during the day before analysis. Blood for immunohematological analysis should be drawn from a vein into a purple tube with EDTA (without shaking).
In this type of laboratory study, the preanalytical stage accounts for about 50% of errors. As in the case with other analyzes, this is due to a violation of the rules for the collection, processing and transportation of material, as well as improper preparation of the patient.
Rules for the primary processing of biomaterial
A separate group of rules for the preanalytical stage of laboratory research is devoted to the primary processing of biomaterial, on which the correct identification of the sample with the patient depends. In addition, some principles of the developed system allow visually standardizing various types of samples. This is especially evident in the variety of containers used for blood collection, where the color of the tubes corresponds to a certain type of study or characterizes the presence of excipients.
Matching the color of the tube with the type of blood sample| Red / white | It does not contain additives, it is used for clinical, chemical and serological studies, as well as serum |
| Green | Contains heparin, intended for plasma and clinical-chemical analysis |
| Purple | Contains EDTA, intended for plasma and hematological studies |
| Gray | Used in tests to determine glucose and lactate, contains sodium fluoride |
Identification marking of biomaterial samples is carried out using barcodes in which the patient's full name is encrypted, the name of the medical department, the name of the doctor and other information. In small institutions, it is permissible to use a manual encoding, presented in the form of numbers or conventional signs, applied to containers containing samples.
In addition to identification marking, the primary processing of biomaterial includes measures aimed at maintaining the stability of the sample until the time of examination (blood centrifugation, inactivation of nucleases, the use of a solution of thiolate-fluorine formalin for concentration and preservation of parasites, etc.).
Storage and transportation conditions for biomaterial
The nature of the requirements contained in this section is based on the conditions under which the biomaterial taken from the patient loses stability to the point where the study becomes impossible or gives an inadequate result.
The maximum shelf life of the material is determined by the period of time during which the analytes correspond to the initial state in 95% of the samples. The allowable limit of sample instability should not be higher than half the value of the total determination error.
Storage and transportation rules are aimed at ensuring optimal physical and chemical conditions (light, temperature, degree of mechanical impact, functional additives, etc.), under which the sample is best kept stable. However, even taking into account modern technologies and techniques, it is artificially impossible to maintain biomaterial in a state adequate for research for a long time. Therefore, the suitability of the samples greatly depends on how quickly they arrive at the diagnostic laboratory.
High requirements for the speed of delivery of samples in CDL are presented to materials intended for microbiological research. The shelf life of such samples should not exceed 2 hours. The regulatory document contains a table in which for each type of biomaterial (blood, cerebrospinal fluid, etc.), the delivery method and temperature of the sample are indicated.
At present, the technological equipment of even the most advanced medical transport systems cannot replace the effectiveness of quick access of samples to research.
Compliance with the storage and transportation methods not only contributes to the suitability of samples for analysis, but also ensures the safety of medical personnel when working with infectious hazardous biomaterials.
Patient Memo
An essential condition for ensuring the quality of laboratory tests at the preanalytical stage is the correct preparation of the patient for analysis, which is based on detailed and adequate information from the side of the clinician and nurse. The instruction includes 2 key parameters:
- explanation of the need for analysis;
- training scheme.
The patient leaflets serve as an effective supporting material for informing the preparatory stage of the preanalytical stage of laboratory diagnostics. They are developed individually for each type of study. In the memo, the purpose of the analysis is usually indicated and the procedure for preparing for the procedure is described. In this case, the patient is reminded of the importance of following these recommendations.