The content of D-dimer and platelets as predictors of an unfavorable outcome in the critical course of COVID-19: a single-center

Research Objective. The aim of this study is to comprehensively assess D-dimer and platelet (PLT) levels in patients with severe and critical COVID-19, analyze their correlation with the intensity of the inflammatory response and disease severity, and identify the days of stay in the intensive care unit (ICU) associated with the highest risk of unfavorable outcomes. Materials and Methods. A total of 70 individuals were examined: the study group included 50 COVID-19 patients (age 45,5 [32–48] years), and the control group consisted of 20 healthy volunteers (age 42,5 [34–47.5] years). The study group was further divided into two subgroups: severe course (Subgroup I, survivors, n = 30) and critical course (Subgroup II, deceased, n = 20). Venous blood levels of D-dimer, PLT, leukocytes (WBC), and C-reactive protein (CRP) were measured in COVID-19 patients on days 3, 5, 7, 10, and 16 of the disease, while the control group was assessed once. The respiratory index (RI) and its correlation with D-dimer and PLT levels were evaluated in the study group. Additionally, correlations between WBC/CRP and D-dimer/PLT levels were analyzed. Statistical analysis was performed using Student’s t-test, ANOVA, Spearman’s correlation, and ROC analysis. Results. Elevated D-dimer levels were observed, with peak values in the deceased subgroup on day 10 (2,36 ± 0,11 ng/mL; p < 0,001). At the same time point, Subgroup II exhibited the lowest PLT counts (107,05 ± 5.07 × 10⁹/L; p < 0,001). A significant correlation was found between high D-dimer levels and thrombocytopenia compared to elevated WBC and CRP levels, as well as between D-dimer/PLT and RI on days 7 and 10 in the deceased subgroup. ROC analysis identified optimal prognostic cut-off values for mortality: D-dimer >1,41 ng/mL and PLT <126,0 × 10⁹/L on day 7 of the disease. Conclusion. High D-dimer levels and thrombocytopenia in the setting of systemic inflammation indicate thromboinflammation and coagulopathy in critically ill COVID-19 patients, serving as unfavorable prognostic markers. A D-dimer level >1,41 ng/mL and PLT count <126,0 × 10⁹/L by day 7 of ICU admission may predict fatal outcomes in critical COVID-19 cases.