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.