Association of systemic inflammation response index and triglyceride-glucose index with the severity of coronary artery stenosis in elderly patients: a retrospective cross-sectional study

Background Atherosclerosis is significantly influenced by chronic inflammation and insulin resistance (IR). This study aims to explore the effects of the Systemic Inflammation Response Index (SIRI) and the Triglyceride-Glucose Index (TyG) on the severity of coronary artery stenosis in patients with coronary artery disease (CAD). Methods This study is a retrospective cross-sectional study conducted at a single center, including 1,019 CAD patients. Based on the median Gensini score, patients were divided into low stenosis (Gensini score < 30) and high stenosis (Gensini score ≥ 30) groups. Logistic regression, interaction analysis, receiver operating characteristic (ROC) curve, Spearman correlation analysis, mediation analysis, and sensitivity analysis using Gensini score tertiles were used to explore the relationship between SIRI, TyG, and the severity of coronary artery stenosis. Results Multivariable logistic regression analysis revealed that SIRI (OR: 1.231, 95% CI: 1.025–1.489, P = 0.006) and TyG (OR: 2.458, 95% CI: 1.737–3.502, P < 0.001) were significantly associated with severe stenosis. Based on the median values of SIRI (0.961) and TyG (8.620), participants were divided into four groups, with the low SIRI + low TyG group as the reference. The OR for the high SIRI + high TyG group was 4.912 (95% CI: 3.185–7.649, P < 0.001). A significant additive interaction between SIRI and TyG was observed, with RERI: 1.947 (95% CI: 0.208–4.103), API: 0.396 (95% CI: 0.042–0.616), and S: 1.991 (95% CI: 1.067–4.430). The inclusion of SIRI and TyG significantly improved predictive performance compared to the traditional risk model, with a Net Reclassification Improvement (NRI) of 0.334 ( P < 0.001) and an Integrated Discrimination Improvement (IDI) of 0.036 ( P < 0.001). Spearman correlation analysis confirmed significant positive correlations of SIRI ( ρ = 0.435, P < 0.001) and TyG ( ρ = 0.347, P < 0.001) with the continuous Gensini score. In the mediation analysis, TyG accounted for 46.7% of the association between SIRI and severe stenosis via a significant indirect statistical association, while SIRI accounted for 21.3% of the association between TyG and severe stenosis via a significant indirect statistical association. Sensitivity analysis using Gensini tertiles confirmed that both SIRI (OR: 1.371, 95% CI: 1.181–1.591, P < 0.001) and TyG (OR: 1.491, 95% CI: 1.181–1.883, P < 0.001) remained independently associated with higher stenosis severity. Conclusion SIRI and TyG are important indicators for predicting the risk of coronary artery stenosis, with an interaction between them, and they exhibit significant indirect statistical associations with each other.