Complete blood count as a tool for risk stratification in COVID-19

BACKGROUND: The causative agent of coronavirus disease (COVID-19) continues to circulate in the population and causes severe cases. A favorable outcome depends on timely assessment of disease severity in the early stages, prompt hospitalization, and appropriate therapeutic adjustments. The complete blood count, performed during initial diagnostics, has proven to be one of the most important tools for assessing disease severity. AIM: The study aimed to evaluate quantitative and calculated complete blood count parameters depending on disease severity at hospital admission and over time, and to identify predictors of adverse outcomes. METHODS: A retrospective analysis was conducted of medical records from 122 patients admitted between March and July 2021 to the N. V. Sklifosovsky Research Institute for Emergency Medicine with confirmed COVID-19 (severe course) within 3 days of symptom onset. Based on outcomes, all patients were divided into 2 groups: group 1, survivors; and group 2, deceased. All patients underwent venous blood sampling at admission and on day 7 of hospitalization, with analysis performed using the ADVIA 2120i hematology analyzer. Additionally, the neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio, and systemic inflammation index were calculated. Quantitative and calculated complete blood count parameters were assessed relative to reference values and compared between groups over time. Statistical analysis was performed using SPSS 20.0 and MedCalc 11.5.00. RESULTS: Compared with group 1, patients in group 2 had higher absolute leukocyte and neutrophil counts and lower lymphocyte and eosinophil counts at all time points. Platelet count showed divergent trend: in group 1, there was a tendency toward an increase by day 7, whereas group 2 demonstrated a consistent decrease. Erythrocyte sedimentation rates were comparable between the groups in the early stages of the disease, but by day 7, a marked increase and a decrease were observed in group 2 and in group 1, respectively. The most informative parameters were the neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio, and systemic inflammation index, which showed statistically significant intergroup differences and were consistently higher in group 2 at all time points. CONCLUSION: Lymphocyte count and neutrophil-to-lymphocyte ratio are early sensitive bioindicators that reflect disease severity, treatment effectiveness, and prognosis in COVID-19.