Association between the blood urea nitrogen to albumin ratio and 30-day mortality in critically ill children with acute kidney injury

Acute kidney injury (AKI) is common in the pediatric intensive care unit (PICU). The blood urea nitrogen to albumin ratio (BAR) is an emerging prognostic marker for critically ill patients. However, its association with outcomes in critically ill children with AKI remains unclear. Pediatric patients with AKI and available BAR measurements were identified from the Pediatric Intensive Care (PIC) database. The primary outcome was 30-day all cause mortality. Multivariate Cox regression analysis was used to clarify the relationship between BAR and the primary outcome. Receiver operating characteristic (ROC) curve analysis was performed to compare the predictive ability of BAR against its components and a referenced biomarker. Kaplan-Meier survival analysis, restricted cubic splines, and stratified analysis were used to verify the findings. The study included 1778 pediatric AKI patients. A significant positive association was observed between BAR and 30-day mortality (HR 1.15, 95% CI 1.05–1.25, p < 0.01). Further analysis revealed a significant non-linear relationship, with an identified inflection point at BAR = 2.49. Based on the optimal cutoff value of 4.07 identified by ROC curve analysis, patients were stratified into a high BAR group and a low BAR group. After multivariate adjustment, the high BAR group showed significantly increased mortality compared to the low BAR group (HR 1.87, 95% CI 1.24–2.84, p < 0.01), a finding that was further supported by a significant separation in Kaplan-Meier survival curves. Subgroup analyses confirmed the robustness of this association across sex, age, and comorbidity subgroups. An elevated BAR was independently associated with short-term mortality in critically ill children with AKI. As a readily available biomarker, BAR may hold potential for risk stratification. Nevertheless, its clinical utility necessitates further validation in prospective studies.