Association between blood urea nitrogen levels and mortality in critical acute ischemic stroke patients.

This retrospective cohort study examined the association between admission blood urea nitrogen (BUN) levels and mortality in critically ill acute ischemic stroke (AIS) patients from the MIMIC-IV database. Patients were stratified into quartiles based on admission BUN (Q1: ≤ 14 mg/dL; Q2:14 < BUN ≤ 19 mg/dL; Q3:19 < BUN ≤ 27 mg/dL; Q4:>27 mg/dL). Multivariable Cox regression, adjusted for demographics, comorbidities, and labs, showed elevated BUN was independently associated with higher 30-day (HR = 1.017, 95% CI: 1.010-1.025), 90-day (HR = 1.014, 1.007-1.021), and 180-day mortality (HR = 1.011, 1.004-1.018). The critically ill AIS patients in the top BUN quartile (> 27 mg/dL) had a nearly 70% higher 30-day, 45% higher 90-day, and 36% higher 180-day mortality risk than those in the bottom quartile, even after full adjustment. Restricted cubic spline analysis demonstrated a linear dose-response relationship between BUN and mortality. Subgroup analysis showed a significant interaction between BUN and CKD: elevated BUN predicted mortality in non-CKD patients but had limited prognostic value in CKD patients. Notably, BUN elevation correlated more strongly with mortality in non-CKD patients. These findings suggest BUN may be an independent predictor useful for risk stratification in critically ill AIS populations, emphasizing its prognostic utility in non-CKD individuals. Further prospective studies are warranted to validate clinical applications and explore underlying mechanisms linking BUN to adverse outcomes.