Remnant cholesterol inflammatory index and cardiovascular disease among adults with cardiovascular-kidney-metabolic syndrome stages 0–3: a nationwide prospective cohort study

The remnant cholesterol inflammatory index (RCII), integrating lipid and inflammatory pathways, may serve as a novel biomarker for cardiovascular risk. Yet, its role in adults across cardiovascular-kidney-metabolic (CKM) syndrome stages 0–3 remains unclear. We included 6,062 participants aged ≥ 45 years and free of cardiovascular disease at baseline from the China Health and Retirement Longitudinal Study (CHARLS). RCII was calculated as remnant cholesterol × high-sensitivity C-reactive protein/10 and log-transformed (lnRCII). Incident cardiovascular disease (CVD) events were ascertained through follow-up interviews (2011–2020). Cox proportional hazards models estimated hazard ratios (HRs) for CVD across lnRCII tertiles and per 1-standard-deviation (SD) increase, adjusting sequentially for demographic and lifestyle factors. Restricted cubic splines, Kaplan–Meier curves, and subgroup analyses were performed. During a median 9-year follow-up, 1751 CVD events occurred (cumulative incidence 28.9%). Higher lnRCII was consistently associated with elevated CVD risk. Each 1-SD increment corresponded to a 9% higher risk in crude and minimally adjusted models (HR 1.09, 95% CI 1.06–1.12), and a 5% higher risk after full adjustment (HR 1.05, 95% CI 1.01–1.08). Cox proportional hazards regression analysis demonstrated that, after adjustment for confounders, the risk of CVD was significantly higher in Q3 than in Q1 (HR 1.22, 95% CI 1.09–1.37, P < 0.001). Spline analysis indicated a linear dose–response, and subgroup findings were broadly consistent across demographic and clinical strata. In additional analyses, lnRCII’s ability to identify cardiovascular events is very poor (AUC = 0.557). After adding lnRCII to the traditional risk model, the C index, net reclassification improvement and comprehensive identification improvement have little change. Elevated lnRCII was associated with an increased risk of incident CVD among adults with CKM stages 0–3. However, its predictive performance was limited, so RCII should currently be regarded as an epidemiologic marker rather than a stand-alone tool for individual risk stratification.