Association between systemic inflammatory response index and the severity of coronary artery lesions in patients undergoing coronary angiography for the first time

Background Inflammation drives coronary artery disease (CAD). The systemic inflammation response index (SIRI) reflects systemic inflammatory status, yet its association with CAD severity in first-time coronary angiography patients remains unclear. Methods This retrospective study included 219 inpatients undergoing initial coronary angiography. CAD severity was quantified by the Gensini score. Patients were divided into SIRI quartiles. Spearman correlation, multivariable linear regression, logistic regression, and ROC analyses were performed. Results Median Gensini scores increased across SIRI quartiles (Q1: 16.75, Q2: 44.00, Q3: 40.00, Q4: 52.00; P < 0.001). SIRI correlated positively with the Gensini score (rho = 0.408, P < 0.001), more strongly than PLR, remnant cholesterol, and RC/HDL-C, with no significant difference vs. neutrophil-to-lymphocyte ratio(NLR), systemic immune-inflammation index(SII), or pan-immune-inflammation value(PIV). In the prespecified primary model adjusting for demographic and clinical confounders, SIRI remained significantly associated with ln(Gensini score+1) ( β = 0.177, 95% CI: 0.089–0.266, P < 0.001); the association was attenuated and no longer statistically significant after additional adjustment for laboratory and lipid parameters ( β = 0.080, 95% CI: −0.021 to 0.182, P = 0.121). Each SIRI unit increase was associated with 2.44-fold higher odds of an above-median Gensini score (>42) (OR = 2.438, 95% CI: 1.544–3.851, P < 0.001). SIRI showed modest discrimination for an above-median Gensini score (AUC: 0.685, 95% CI: 0.615–0.755), numerically the highest among the seven indices but not statistically superior to NLR, SII, or PIV. Subgroup analyses confirmed significant correlations across sex, age, diabetes, and hypertension strata. Conclusions SIRI is positively associated with angiographic CAD severity in patients undergoing first-time coronary angiography. As an inexpensive biomarker derived from routine blood counts, SIRI may serve as an adjunctive tool for pre-procedural risk stratification in this specific population.