Elevated blood urea nitrogen-to-albumin ratio is associated with incident sepsis-associated delirium: evidence from a weighted competing-risk analysis in a multicenter cohort study.

Background: Sepsis-associated delirium (SAD) is a frequent manifestation of acute brain dysfunction in sepsis. Although the blood urea nitrogen-to-albumin ratio (BAR) has been associated with prognosis in critically ill patients, its relationship with incident SAD remains uncertain. We evaluated the association between early BAR and incident SAD. Methods: This multicenter retrospective cohort study included patients with sepsis from MIMIC-IV as the primary cohort and eICU-CRD as an independent replication cohort. BAR was calculated from eligible blood urea nitrogen and serum albumin measurements obtained within 24 h after the index time. The primary outcome was 7-day incident delirium; 3-day delirium was additionally evaluated in MIMIC-IV. Death before delirium was treated as a competing event. Covariates were selected using Boruta and LASSO regression. CBPS-based inverse probability weighting and Fine-Gray competing-risk regression were applied, with restricted cubic spline, subgroup, and exploratory XGBoost/SHAP analyses. Results: A total of 10,565 patients were included (9,612 MIMIC-IV; 953 eICU-CRD). In MIMIC-IV, the highest BAR quartile was associated with a greater subdistribution hazard of 7-day delirium vs. the lowest quartile (fully adjusted sHR 1.36, 95% CI 1.13-1.64; Conclusion: Higher early BAR, particularly values in the highest quartile, was associated with a greater subdistribution hazard of incident SAD, and the highest-quartile association was independently reproduced in eICU-CRD. BAR may serve as a simple risk-associated marker for identifying patients with sepsis at higher risk of incident delirium.