The prognostic value of red cell distribution width-to-albumin ratio (RAR) in COVID-19 pneumonia: implications for early diagnosis

PURPOSE: This study aimed to evaluate the diagnostic value of red blood cell distribution width-to-albumin ratio (RAR), a biomarker integrating hematological and metabolic information, for COVID-19 pneumonia. METHODS: This retrospective study analyzed clinical data from 2,205 patients with COVID-19. RAR values were calculated as the ratio of red blood cell distribution width (RDW) to serum albumin concentration. Diagnostic performance of RAR in COVID-19 pneumonia was assessed using receiver operating characteristic (ROC) curve analysis, and the optimal cut-off was determined. Mediation analysis was conducted to examine the role of chronological age in the association between RAR and COVID-19 pneumonia risk. RESULTS: Among COVID-19 patients, RAR demonstrated strong diagnostic performance for COVID-19 pneumonia, with area under the curve (AUC) of 0.769 [95% confidence interval (CI): 0.747-0.791], sensitivity of 76.8%, and specificity of 65.3% at the optimal cut-off value of 0.154. Its diagnostic utility likely stems from simultaneously reflecting hematopoietic dysfunction (elevated RDW) and systemic metabolic imbalance (hypoalbuminemia). Mediation analysis indicated that chronological age accounted for 14.16% of the association between elevated RAR and COVID-19 pneumonia risk (β = 0.1139, 95%CI: 0.0802-0.1524). CONCLUSION: RAR represents a promising biomarker for the early detection and risk stratification of COVID-19 pneumonia. By simultaneously capturing hematologic and metabolic disturbances, RAR provides a more comprehensive reflection of disease severity. The observed age-mediation effect suggests that elderly individuals with elevated RAR may face heightened risk, warranting enhanced clinical monitoring or prioritized intervention.