Association between the blood urea nitrogen–to–serum albumin ratio and all-cause mortality in critically ill patients with hypertension: a retrospective cohort study of MIMIC-IV database

Background This study aims to investigate the association between the blood urea nitrogen–to–albumin ratio (BAR) and short- and long-term all-cause mortality in critically ill patients with hypertension admitted to the intensive care unit. Methods A retrospective cohort study was conducted using data from the Medical Information Mart for Intensive Care IV database, which includes ICU patients from 2008 to 2022. Patients with hypertension were identified using ICD codes and categorized into quartiles according to BAR values. Kaplan–Meier survival analyses were performed to compare mortality across BAR quartiles. Multivariate Cox regression models were employed to assess the association between BAR and 30-day, 90-day, and 365-day mortality. Receiver operating characteristic curve was plotted to evaluate the predictive value of BAR, BUN, and SOFA for mortality outcomes. Subgroup analyses were conducted based on comorbidities and clinical characteristics. The external validation was performed in eICU 2.0 database. Results A total of 8,538 patients with hypertension were included. The 30-day, 90-day, and 365-day mortality rates were 20.3%, 26.6%, and 35.5%, respectively. Kaplan–Meier analyses demonstrated progressively higher all-cause mortality across increasing BAR quartiles (log-rank p < 0.001). In fully adjusted Cox models, patients in the highest BAR quartile (Q4) exhibited significantly higher risks of all-cause mortality compared with those in the lowest quartile (Q1), including 30-day mortality (HR 1.92, 95% CI: 1.58–2.32; p < 0.001), 90-day mortality (HR 1.86, 95% CI: 1.58–2.20; p < 0.001), and 365-day mortality (HR 1.70, 95% CI: 1.48–1.96; p < 0.001). The area under the curve (AUC) for BAR in predicting 30-day, 90-day, and 365-day mortality was 0.653, 0.655, and 0.652, respectively. Subgroup analyses demonstrated generally consistent associations across most strata. In the external eICU validation cohort including 6,644 hypertensive patients, higher BAR quartiles were independently associated with increased in-hospital all-cause mortality, while a similar but non-significant risk-increasing trend was observed for in-ICU mortality. Conclusion Higher BAR levels were associated with increased short- and long-term all-cause mortality in critically ill patients with hypertension. BAR may provide incremental information for risk assessment in this population; however, further prospective studies are warranted to confirm its clinical utility.