Abstract
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 × 10(11)/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.