Association of the novel remnant cholesterol inflammatory index with acute coronary syndrome risk in hospitalized patients with diabetes: a two-center study

Remnant cholesterol and low-grade inflammation are key contributors to acute coronary syndrome (ACS) in patients with diabetes mellitus. The novel remnant cholesterol inflammatory index (NRCII), combining remnant cholesterol (RC) and the neutrophil-to-lymphocyte ratio (NLR), may enhance risk stratification, but its clinical relevance in diabetic inpatients remains unclear. This multicenter retrospective study included 3664 diabetic inpatients hospitalized between August 2019 and June 2025. Logistic regression, restricted cubic spline (RCS), subgroup, and sensitivity analyses were conducted to assess the association between NRCII and ACS. Incremental predictive value was evaluated using C-statistic, net reclassification improvement (NRI), integrated discrimination improvement (IDI), and likelihood-ratio (LR) tests. ACS occurred in 1056 participants (28.8%). Each 1-unit increase in NRCII was associated with a 21% higher risk of ACS in the fully adjusted model (OR = 1.21, 95% CI 1.13-1.29, P < 0.001). Quartile analyses showed a clear dose-response (P for trend < 0.001), with the highest quartile showing nearly three-fold greater risk (OR = 2.78, 95% CI 1.86-4.04) compared to the lowest. RCS confirmed a significant nonlinear positive association. Results remained robust after excluding patients on lipid-lowering therapy. Subgroup analyses revealed interactions with age and alcohol use. NRCII addition to the clinical model provided the greatest performance gain (C-statistic 0.751; NRI 0.271; IDI 0.020; LR 30.63; all P < 0.001) over RC or NLR alone. Higher NRCII is independently and strongly associated with ACS risk among hospitalized patients with diabetes, offering superior predictive value compared to RC or NLR alone. NRCII may serve as a simple, effective tool for ACS risk stratification in this high-risk population.