Currently, laboratory diagnostics is a multifaceted enterprise with its own control mechanisms and technologies of different levels of complexity. Despite the introduction of advanced automated analytical systems, errors are recorded in laboratory medicine, the percentage of which is difficult to calculate due to the fact that they are difficult to determine and it is impossible to establish their relationship to the cause of their occurrence. However, research data indicate that most errors are recorded in the out-of-laboratory part of the preanalytical stage. This is due to the fact that the extra-laboratory part of the preanalytical stage includes a number of procedures (assignment of laboratory tests, collection, storage and transportation of biomaterial), which require the involvement of a large number of personnel of medical organizations and are outside the control of laboratory staff. Refusal of laboratory tests, as a rule, is associated with poor quality of biomaterial coming to the laboratory. The most common reasons for rejection are hemolyzed samples, insufficient or inadequate volume of biomaterial, biological samples collected in inappropriate tubes, and clots in samples with anticoagulants. This leads to a delay in obtaining a reliable result and making a timely correct diagnosis, and also entails the economic cost of repeated biomaterial collection.