Combined discriminative value of SII and sdLDL-C for 1-year major adverse cardiovascular events in patients with unstable angina pectoris

Objective To assess the associations of the systemic immune-inflammation index (SII) and small dense low-density lipoprotein cholesterol (sdLDL-C) with 1-year major adverse cardiovascular events (MACE) in patients with unstable angina pectoris (UAP) and to evaluate their individual and combined discriminative performance. Methods This single-center retrospective cohort study included 157 patients diagnosed with UAP who underwent coronary angiography between January 2022 and June 2024. Routine blood counts, lipid profiles, and electrocardiography were obtained within 24 h after admission. SII was calculated as neutrophil count × platelet count/lymphocyte count. The prespecified endpoint was the occurrence of at least one MACE during the fixed 1-year follow-up period, including cardiac death, nonfatal myocardial infarction, target vessel revascularization, or rehospitalization for worsening heart failure. Patients were classified into the MACE group ( n = 38) and the non-MACE group ( n = 119). Variables showing statistical significance in the univariable analyses were entered into a multivariable logistic regression model to identify factors independently associated with 1-year MACE. Receiver operating characteristic curves were used to assess the discriminative performance of SII, sdLDL-C, and their combination. Internal validation was performed using 1,000 bootstrap resamples. Results Compared with the non-MACE group, patients in the MACE group were older, had a higher prevalence of diabetes mellitus, higher Gensini scores, and more frequent multi-lead ischemic changes on electrocardiography. The MACE group also had higher WBC, NEUT, PLT, SII, TG, and sdLDL-C levels and lower LYM levels (all P < 0.05). Multivariable logistic regression showed that SII ≥ 1,100 (OR = 3.58, 95% CI: 1.79–7.14; P < 0.001), sdLDL-C ≥ 1.02 mmol/L (OR = 2.91, 95% CI: 1.42–5.97; P = 0.003), Gensini score ≥ 45 points (OR = 2.67, 95% CI: 1.31–5.46; P = 0.006), and multi-lead ischemic changes (OR = 2.43, 95% CI: 1.18–5.01; P = 0.017) were independently associated with 1-year MACE. The AUCs of SII, sdLDL-C, and the combined SII–sdLDL-C model were 0.832, 0.789, and 0.914, respectively. After bootstrap validation, the optimism-corrected AUC of the combined model was 0.893, with a calibration slope of 0.87. Conclusion Elevated SII and sdLDL-C levels were independently associated with MACE within 1 year in patients with UAP. Their combination showed better discrimination than either marker alone. However, because of the limited number of patients with MACE and the absence of external validation, these findings should be considered exploratory and require confirmation in larger prospective multicenter cohorts.