Association between blood urea nitrogen-to-albumin ratio and postoperative acute kidney injury in patients undergoing off-pump coronary artery bypass grafting: a retrospective observational study

Acute kidney injury (AKI) is a common complication after off-pump coronary artery bypass grafting (OPCABG). Although the blood urea nitrogen-to-albumin ratio (BAR) has shown prognostic value in other settings, its association with postoperative AKI in OPCABG remains unclear. Multivariable logistic regression was used to evaluate the association between BAR and postoperative AKI. Predictive performance was assessed using receiver operating characteristic (ROC) analysis and calibration, with internal validation by bootstrap resampling. Incremental value was evaluated using net reclassification improvement (NRI), integrated discrimination improvement (IDI) and decision curve analysis (DCA). Inverse probability of treatment weighting (IPTW) and sensitivity analyses were conducted to examine robustness. BAR was independently associated with postoperative AKI, both as a continuous variable (per 1-standard deviation [SD] increase: odds ratio [OR] 1.90, 95% confidence interval [CI] 1.58–2.27) and as a categorical variable (BAR≥ 0.2 mmol/g: OR 4.56, 95% CI 2.99–6.94). This association remained robust in IPTW and sensitivity analyses. Adding BAR improved discrimination (AUC: 0.754 vs. 0.694; ΔAUC = 0.060, p < 0.001) with stable performance after bootstrap validation. Reclassification and DCA further supported its potential value for early AKI risk stratification. Elevated preoperative BAR was independently associated with an increased risk of postoperative AKI and may serve as a useful risk marker in patients undergoing OPCABG.