Systemic immune-inflammation index as a promising predictor of mortality in patients with acute coronary syndrome: a real-world study

OBJECTIVE: Prognostic indicators in acute coronary syndrome (ACS) would aid in decision-making and identifying high-risk patients. The systemic immune-inflammation index (SII) has good prognostic value in many diseases; however, its use has not been reported for ACS. We aimed to determine the associations between the SII and outcomes in patients with ACS, with adjustment for confounders. METHODS: In this retrospective cohort study, we used the MIMIC-III (Multiparameter Intelligent Monitoring in Intensive Care) database and the eICU Collaborative Research Database. The primary outcome was 30-day mortality. Cox regression analysis was performed to determine the relationship between the SII and patient outcomes, and we conducted subgroup analysis and smooth curve fitting. RESULTS: We identified 4699 patients with ACS: 1741 women and 2949 men, mean age 82.8±29.7 years, and mean SII 72.58±12.9. For 30-day all-cause mortality, the unadjusted hazard ratio (HR) (95% confidence interval [CI]) of SII <69.4 and SII >88.8 were 1.25 (1.04, 1.50) and 1.38 (1.15, 1.65), respectively. With SII >88.8, this association remained significant after adjustment for numerous potential confounders: HR 1.27 (1.06, 1.52). A similar relationship was observed for 90-day and 1-year all-cause mortality. CONCLUSIONS: SII is a promising prognostic indicator for unselected patients with ACS. This finding needs to be confirmed in prospective studies.