The review shows the importance of studying laboratory indicators that could be predictors of the development of the COVID-19 severe and adverse course. Pathological coagulation was observed in severely ill patients. The coagulation activation might be associated with a sustained inflammatory response. The infection-related biomarkers differed in patients with severe and mild COVID-19. The C-reactive protein and procalcitonin, other pro-inflammatory cytokines and indicators of the immune response levels are important indicators for developing the treatment strategy. The combined detection of interleukin-6 and D-dimers is a good predictor of severe COVID-19. Attention is paid to the adverse outcomes of COVID-19 correlation with the hypercoagulation severity, cardiac abnormalities and myocardial damage, hematopoiesis disorders against the septic state and endotoxemia, and the intensity of the systemic inflammatory process.