Bridging the gap between biomarkers and bedside decisions: the prognostic value of the blood urea nitrogen-to-albumin ratio in sepsis-associated AKI

Background While sepsis-associated acute kidney injury (AKI) is a leading cause of mortality in intensive care units, identifying high-risk patients remains clinically challenging. Traditional severity scores often fail to capture dynamic metabolic disturbances. This study aimed to characterize the association between the blood urea nitrogen-to-albumin ratio (BAR)—a novel biomarker reflecting systemic nitrogen metabolism and nutritional status—and 28-day mortality in patients with sepsis-associated AKI undergoing continuous renal replacement therapy (CRRT). Methods This prospective observational study included 790 patients with sepsis-associated AKI undergoing CRRT. log 2 BAR was evaluated as a candidate prognostic variable. Multivariable Cox proportional hazard regression models were used to determine the association with 28-day mortality. The dose–response relationship was characterized by restricted cubic splines (RCS). The prognostic accuracy and incremental predictive value of log 2 BAR beyond traditional risk models were assessed using the area under the receiver operating characteristic curve (AUC), net reclassification improvement (NRI), and integrated discrimination improvement (IDI). Calibration and clinical utility were further evaluated using calibration curves and decision curve analysis (DCA). Model robustness was validated through subgroup analyses, categorical stratification, and E-value quantification to assess potential unmeasured confounding. Results Multivariable analysis identified log 2 BAR as an independent predictor of 28-day mortality (adjusted HR = 1.33, 95% CI: 1.15~1.53, P < 0.001). RCS analysis revealed a significant dose–response relationship, with mortality risk increasing monotonically with log 2 BAR. The integration of log 2 BAR into traditional risk models significantly improved prognostic accuracy (AUC increased from 0.772 to 0.783, P < 0.05). Sensitivity analyses, including categorical stratification and E-value calculations, confirmed the robustness of these findings against potential unmeasured confounders across different Modelspecifications and population subsets. Conclusions log 2 BAR is a robust and independent predictor of 28-day mortality in patients with sepsis-associated AKI treated with CRRT. Integrating this readily available biomarker provides valuable prognostic precision, supporting its use as a supplementary prognostic tool for early risk stratification in critically ill patients.