Introduction. The pre-analytical phase is key to developing procedures aimed at improving patient safety by reducing the likelihood of errors. The introduction of management tools of quality control helps to evaluate extra-analytical processes, to identify critical aspects develop corrective measures and compare the results with the state-of-the-art practices. Materials and methods. A retrospective study of the quality indicators of the pre-analytical phase included in the quality management system of the Interdistrict Clinical Diagnostic Laboratories of the St. Petersburg State Budgetary Institution Consultative and Diagnostic Center for Children. Data on 18 quality indicators were extracted over a period of one year from January 2017 to December 2018. The indicators were formed taking into account the type of biological material, the incoming biomaterial to the laboratory of the Interdistrict Clinical Diagnostic Laboratories of the St. Petersburg State Budgetary Institution Consultative and Diagnostic Center for Children from the treatment room and 35 contractors, including 14 children’s and 21 adult medical organizations. The results of the quality indicators were expressed in percentages (median) and sigma (sigmametrics). Results. It has been established that the majority of quality indicators of the pre-analytical phase are in the range of 4—5 sigma, which indicates a satisfactory quality of the studied processes. Values ranging from 3.6 to 3.7 sigma over the course of two years were obtained by a single quality indicator, evaluating the presence of hemolysis in a blood serum sample. However, none of the indicators reached a level of 6 sigma. Conclusions. The use of quality indicators is widely used when developing strategies to help identify and manage risks. A systematic assessment of quality indicators using the Six Sigma calculation is an objective criterion that allows for a timely assessment of the quality of not only analytical but also pre-analytical processes.