External quality assessment, conducted in the form of interlaboratory comparisons, is traditionally a tool for verifying laboratory qualifications and confirming the level of measurement accuracy required or claimed by laboratories. The authors identified industry-specific measurement features in laboratory medicine and analyzed long-term participation in the external quality assessment system. Based on these data, the authors concluded that in the absence of appropriate standards, certified reference materials and reference methods for many analytes, the external quality assessment system for medical laboratories acquires a different meaning and becomes an indispensable tool for obtaining objective data on the reproducibility/ consistency of the results obtained in different laboratories, identifying biases in the measurement results of participating laboratories. In such circumstances, an external quality assessment confirms the qualification of a medical laboratory in using a specific analytical technique in combination with reference clinical information corresponding to this particular technique. The results obtained may be of interest to specialists working at the interface of metrology and clinical laboratory diagnostics, as well as manufacturers of medical devices for in vitro diagnostics and external quality assessment providers.