Association between red blood cell distribution width to albumin ratio and prognosis in patients with sepsis-associated acute kidney injury: a retrospective cohort study

Background The red blood cell distribution width-to-albumin ratio (RAR) has shown prognostic value in sepsis, diabetes comorbidities, and cancer (CA). However, its relevance to clinical outcomes in sepsis-associated acute kidney injury (SA-AKI) remains unclear. This study aimed to explore this relationship. Methods A retrospective cohort study was conducted on SA-AKI patients admitted to the Intensive Care Unit of Baise People's Hospital, Guangxi, from May 2022 to May 2025. The primary endpoint was 28-day all-cause mortality. The prognostic utility of RAR was assessed using multivariable Cox regression, restricted cubic splines (RCS), Kaplan–Meier survival curves with log-rank tests, stratified analysis, receiver operating characteristic (ROC) curves, subgroup, and sensitivity analyses. Results Among the 161 enrolled patients (mean age 63.7 ± 16.6 years), the mean RAR was 6.95 ± 2.81%/g/dl. A linear association between RAR and mortality was observed (non-linearity p = 0.162). After multivariable adjustment, the highest RAR quartile (Q4: >8.31) was associated with a hazard ratio (HR) of 7.52 (95% CI: 2.24–25.29) compared to Q1 (< 5.07). Kaplan–Meier analysis revealed significantly higher mortality in the high-RAR groups ( p < 0.001). The area under the ROC curve (AUC) for RAR in predicting 28-day mortality was 0.694 (95% CI: 0.612–0.776). Combining RAR with the lactate-to-albumin ratio (LAR) significantly enhanced predictive accuracy (AUC: 0.777; 95% CI: 0.703–0.851; p = 0.043 vs. RAR alone). Conclusion Elevated RAR independently predicts adverse early prognosis in SA-AKI, with higher levels correlating with increased 28-day mortality. The combination of RAR and LAR significantly improves mortality prediction in this cohort.