Critical values in medical laboratory require great care about both laboratory personnel and clinicians. The Aim of the study was to establish the rate of patients with critical values (CV) in different healthcare organizations, the quantity of critical values in different analytes and the departments in which patients with high rate of CV are placed. Besides, the aim was to evaluate the possibility of critical values interpretation in the context of the out-of-laboratory preanalytical phase in each clinic. Material and methods. 6 medical organizations took part in the pilot study. The data collected for 12 months were used for analysis. Critical values were chosen in every laboratory using the analytes and their levels of CV list recommended in GOST R 53079.3-2008. The complexity of probes delivery was scaled from 1 to 5 depending on the delivery method and speed, from the easiest one (1) with a one-hour delivery to the same building and to the hardest one (5+) with having a number of counterachtants and using delivery services including railway transportation. Results and conclusion. We understand that with a little quantity of participants it is statistically impossible to make a generalized conclusion but taking in account the deficit of publications in Russian we suppose we can comment the results. The 30-time difference for hospital inpatients and outpatients with CV in different clinics pays attention to itself. Interpretation difficulties are the consequence of inability to fully estimate the analytical quality level in the range of «critical» concentrations of analytes. There were two preanalytically dependent analytes in CV lists: high potassium levels and low glucose levels. Undoubtly, barrier gel couldn’t prevent from potassium infiltration to serum from blood cells in tubes in terms of long transportation. In opposite, there were no difference between low glucose levels (tubes with glucose inhibitors) in clinics with «complex» and «easy» ways of delivery. It’s also obviously that it’s more complicated to interpret CV in preanalytically dependent analytes in terms of complex way of delivery. The rate of patients with CV in 14 analytes didn‘t exceed 1,67%. In our study, high levels of potassium were highly more often in hospital inpatients than in outpatients (table 3). Probably this is typical (as well as in low potassium) for emergency departments and intensive care units. High frequency of high hematocrit critical levels (1179 cases) more than 60% was associated with a large number of newborns. This confirms the ISO 15189 statement that every medical laboratory should establish their own CV list and levels of CV taking into account patient populations in clinics.