When treating patients with COVID-19, prognostic and diagnostic tests to assess the risk of severe disease and adverse outcome are particularly important. The analysis of demographic, clinical, laboratory and instrumental data obtained on ICU admission was performed on a sample of 109 patients to determine potential predictors of lethal outcome. The factors increasing the risk of adverse outcome included age ≥57 years (AUC = 0.777, P < 0.001), hypertension (RR = 3.073, P = 0.033), ARDS (RR = 17.455, P < 0.001), advanced chest CT severity score (HR = 1.569, P = 0.039), severe and critical COVID-19 (RR = 6.964, P = 0.016), neutrophilia (AUC = 0.729, P = 0.005), lymphopenia (AUC = 0.705, P = 0.023), thrombocytopenia (AUC = 0.713, P = 0.018), reduced MCHC (AUC = 0.700, P = 0.026), elevated RDW (AUC = 0.718, P = 0.007), LDH (AUC = 0.891, P = 0.005) and D-dimer (AUC = 0.806, P = 0.029).