Background: Cardiac surgery-associated acute kidney injury (CSA-AKI) is a common condition, posing significant morbidity and mortality. Combined triglyceride-glucose (TyG) index-body mass index (BMI) may offer enhanced predictive performance for CSA-AKI compared to TyG or BMI alone. Therefore, this study aims to assess whether the preoperative TyG-BMI index outperforms individual TyG or BMI measurements in predicting CSA-AKI.

Methods: This retrospective cohort study included adult patients (n = 652) undergoing cardiac surgery with cardiopulmonary bypass (CPB). The TyG-BMI was calculated as ln[triglyceride (mg/dL) × fasting glucose (mg/dL)/2] × BMI (kg/m²) and CSA-AKI was defined according to Kidney Disease: Improving Global Outcomes (KDIGO) criteria. The discriminative performance of combined TyG-BMI and individual TyG and BMI was compared using receiver operating characteristic (ROC) analysis. These three indicators were incorporated independently into a baseline predictive model, and model performance was examined. Multivariable logistic regression and restricted cubic splines (RCS) were applied to evaluate the association between TyG-BMI and CSA-AKI. Subgroup analyses were performed to assess effect heterogeneity by age, sex, hypertension, diabetes, and other comorbidities.

Results: Among the study cohort (n = 652), CSA-AKI was reported in 34.4% (224/652) of the cases. TyG-BMI showed superior discriminative performance compared to TyG or BMI alone (AUC: 0.712 vs. 0.666 and 0.681; DeLong test p = 0.021 and <0.001, respectively). Incorporating TyG-BMI, TyG, and BMI into the baseline prediction model (AUC: 0.773) increased the AUC to 0.814 for TyG-BMI, 0.794 for TyG, and 0.805 for BMI. RCS indicated a linear association between TyG-BMI and CSA-AKI (p for nonlinearity = 0.496). For every 15-unit increase in TyG-BMI, the risk of CSA-AKI increased by 41% (adjusted OR: 1.41, 95% CI 1.28–1.55; p < 0.001). Patients in the highest TyG-BMI quartile had significantly higher odds of CSA-AKI (adjusted OR: 5.00; 95% CI 2.68–9.35; p < 0.001) compared to those in the lowest quartile. Subgroup analyses confirmed these findings, except in those with diabetes (p = 0.279).

Conclusions: Preoperative TyG-BMI is independently associated with CSA-AKI in a linear dose-response manner. As a cost-effective composite marker of insulin resistance and adiposity, TyG-BMI improves preoperative risk stratification and enables targeted interventions to mitigate postoperative renal injury. Prospective studies are needed to further validate its clinical applicability.

Clinical Trial Registration: Chinese Clinical Trial Registry (ChiCTR2500103685).