Association Between Blood Urea Nitrogen to Serum Albumin Ratio and 28-Day Mortality Risk in Sepsis Patients with AKI Undergoing Continuous Renal Replacement Therapy: A Secondary Analysis Based on a Retrospective Cohort Study

Background : The blood urea nitrogen to albumin ratio (BAR) reflects both metabolic stress and nutritional status and may serve as a valuable prognostic marker in critically ill patients. However, its association with 28-day mortality in sepsis-related acute kidney injury (AKI) remains unclear, particularly among those receiving continuous renal replacement therapy (CRRT). This study aims to evaluate the relationship between BAR and short-term mortality and to explore its clinical relevance in risk stratification for critically ill patients. Methods :This study was a secondary analysis based on a publicly available dataset. A total of 790 critically ill patients with sepsis-associated acute kidney injury who received continuous renal replacement therapy (CRRT) between January 2009 and September 2016 were included. The dataset was obtained from the Dryad repository. The blood urea nitrogen to albumin ratio (BAR) was calculated at the initiation of CRRT, and patients were categorized into tertiles based on BAR values. Cox proportional hazards regression models, restricted cubic spline analysis, and Kaplan–Meier survival curves were used to evaluate the association between BAR and 28-day mortality. To assess the robustness of the findings, subgroup analyses were conducted. Results : Among 790 patients, 494 (62.5%) died within 28 days. Higher blood urea nitrogen to albumin ratio (BAR) was significantly associated with increased 28-day mortality. Patients in the highest tertile (Q3) had a 2.54-fold increased risk compared to those in the lowest tertile (Q1) (HR = 2.54, 95% CI: 1.62–3.98, P < 0.001). Restricted cubic spline analysis revealed a linear dose-response relationship. Kaplan-Meier curves showed significantly lower survival in the Q3 group ( P < 0.001). Subgroup analyses confirmed the robustness of the associations. Conclusions : The blood urea nitrogen to albumin ratio (BAR) is an independent and clinically relevant predictor of 28-day mortality in septic patients with AKI undergoing CRRT. Elevated BAR is associated with significantly increased short-term mortality risk. Monitoring BAR may aid in early risk stratification and inform individualized treatment strategies in critically ill populations.