During the COVID-19 pandemic, laboratory biomarkers have become essential tools for evaluating disease severity, predicting complications, and determining the need for intensive therapy. This article presents a scientific and analytical synthesis of retrospective data from 350 hospitalized patients with PCR-confirmed SARS-CoV-2 infection. Key laboratory indicators with high prognostic significance were identified: lymphopenia, neutrophil-to-lymphocyte ratio (N/L), C-reactive protein (CRP), lactate dehydrogenase (LDH), fibrinogen, D-dimer, and platelet parameters. The study established that combined immuno-inflammatory and coagulopathic abnormalities shape an integral pathogenetic profile of severe COVID-19. Particular attention is given to the U-shaped relationship between fibrinogen levels (9.0 g/L) and mortality risk, as well as the strong association of elevated D-dimer with thrombotic complications and multi-organ failure. These findings underscore the necessity of continuous laboratory monitoring and highlight the importance of biomarker-based personalized patient management.