Acute kidney injury, contrast-induced acute kidney injury, systemic immune-inflammation index, coronary artery disease, nonlinear relationship, biomarker, Diseases of the genitourinary system. Urology, RC870-923

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