Red cell distribution width to albumin ratio (RAR) as a prognostic marker for mortality in critical care patients: a large-scale retrospective cohort study

BACKGROUND: Prognosis of critically ill patients is strongly correlated with nutritional and inflammatory states. This study aimed to evaluate the potential of the red cell distribution width to albumin ratio (RAR) as a mortality predictor in ICU patients, focusing on its prognostic value in diverse patient subgroups. METHODS: In this retrospective cohort study, 24,568 adult ICU patients were analyzed. RAR was calculated upon admission, and the relationship between RAR and 28-day mortality was assessed using Cox proportional hazards modeling and restricted cubic spline analysis to explore nonlinearity. Receiver operating characteristic (ROC) analysis assessed predictive performance, and subgroup analyses examined the prognostic strength of RAR across age groups, disease severity, and required interventions. RESULTS: The predictive power of RAR for 28-day mortality was moderate (AUC = 0.66, 95% CI 0.65-0.67). Multivariate analysis showed that higher RAR values were associated with a higher risk of death (adjusted HR = 1.06, 95% CI 1.05-1.07, P < 0.001) and a significant nonlinear relationship (P < 0.001). Subgroup analyses showed that the prognostic value of RAR was higher in patients aged ≥ 65 years and in patients with a SOFA score of ≥ 6. Combining RAR with SOFA scores improved predictive accuracy (AUC = 0.74, 95% CI 0.72-0.76), suggesting that RAR has the potential to be an adjunct to mortality risk assessment in the ICU setting. CONCLUSIONS: Although RAR demonstrates only moderate predictive ability on its own (AUC = 0.66), it significantly enhances prognostic accuracy when combined with SOFA scores (AUC 0.74), suggesting its role as a complementary rather than independent prognostic tool in ICU risk stratification.