Preoperative systemic immune-inflammation index as a predictor of contrast-induced acute kidney injury in coronary artery disease: a multicenter cohort study

Background Inflammation is a key contributor to contrast-induced acute kidney injury (CI-AKI), yet its predictive role remains unclear. The systemic immune-inflammation index (SII) is a novel inflammatory biomarker, but its association with CI-AKI risk in coronary artery disease (CAD) patients undergoing coronary angiography is not well established. This study aimed to evaluate the relationship between preoperative SII and CI-AKI in a large multicenter cohort.Methods This retrospective cohort study analyzed CAD patients from five tertiary hospitals in China (2007–2020). Patients were stratified into SII tertiles, and multivariable logistic regression, restricted cubic splines (RCS), and two-piecewise logistic regression models were employed to assess the association between SII and CI-AKI risk.Results Among 30,822 patients, 3,246 (10.5%) developed CI-AKI. Higher preoperative SII levels were associated with increased CI-AKI risk ([SII-M vs. SII-L]: OR = 1.22, 95% CI [1.09–1.36], p = 0.001; [SII-H vs. SII-L]: OR = 1.70, 95% CI [1.53–1.90], p < 0.001). RCS analysis demonstrated a nonlinear relationship (p for nonlinearity = 0.008). The inflection point was at 19.12 × 1011/L. Below this inflection point, each 100-unit increase in SII correlated with a 5% higher CI-AKI risk (OR = 1.05, 95% CI [1.04–1.06], p < 0.001), while no significant association was observed above this level.Conclusion Preoperative SII may be an independent predictor of CI-AKI risk in CAD patients undergoing undergoing coronary angiography, demonstrating a nonlinear dose-response relationship with a significant threshold effect. These findings suggest that SII may serve as a useful biomarker for early CI-AKI risk stratification in clinical practice.