The diagnostic value of residual cholesterol inflammatory index for coronary artery disease severity in patients with premature coronary artery disease undergoing percutaneous coronary intervention

To investigate the diagnostic value of the Residual Cholesterol Inflammatory Index (RCII) for assessing coronary artery disease severity in patients with premature coronary artery disease (PCAD) undergoing percutaneous coronary intervention (PCI), and to provide evidence for clinical risk stratification and individualized treatment. A retrospective study was conducted on 351 patients diagnosed with PCAD who underwent PCI at Nantong First People’s Hospital between January 2024 and December 2025. Patients were divided into four groups (low, medium, high, and extremely high RCII) based on RCII quartiles. Baseline characteristics, laboratory parameters, and coronary angiography data were collected. Coronary lesion severity was evaluated using the Gensini score. Associations between RCII and coronary lesion severity were analyzed using the Kruskal‑Wallis H test, χ² test, multiple linear regression, restricted cubic spline (RCS) analysis, and receiver operating characteristic (ROC) curves. With the increase in RCII levels, the Gensini score, the rate of three-vessel coronary artery disease, and the incidence of acute myocardial infarction (AMI) in PCAD patients undergoing PCI increased significantly (all P < 0.001). Multiple linear regression analysis, after adjustment for traditional cardiovascular risk factors, showed that RCII exhibited a significant non-linear (inverted U-shaped) association with Gensini score (P for nonlinearity < 0.001), with a positive linear relationship predominantly observed in the low-to-moderate RCII range (≤ 40, accounting for 94% of the population) (unstandardized regression coefficient B = 0.52, 95% confidence interval 0.338–0.701, P < 0.001). Restricted cubic spline (RCS) analysis revealed a significant inverted U-shaped nonlinear association between RCII and Gensini score (P for nonlinearity < 0.001), with an inflection point threshold of approximately 40. Receiver operating characteristic (ROC) curve analysis showed that the area under the curve (AUC) of RCII for assessing severe coronary artery disease (Gensini score ≥ 60) was 0.698, for three-vessel coronary artery disease was 0.723, and for AMI was 0.598, all of which were significantly higher than those of residual cholesterol (RC) alone (all P < 0.05 for DeLong test). RCII demonstrates moderate predictive ability for coronary lesion severity in PCAD patients undergoing PCI, serving as an independently associated indicator for severe coronary lesions. Its predictive performance is superior to RC alone, making it a potential auxiliary biomarker for risk assessment. While its clinical application value still needs to be further verified in large-sample, multi-center, prospective cohort studies.