Association of systemic immune-inflammation index (SII) with 28-day all-cause mortality in acute heart failure: A retrospective cohort study

This study aimed to investigate the association between the systemic immune-inflammation index (SII) and 28-day all-cause mortality in patients with acute heart failure (AHF) and to evaluate the potential of SII as a prognostic biomarker for early risk stratification. A retrospective cohort study was conducted using the Medical Information Mart for Intensive Care IV database. Patients with an AHF diagnosis on first intensive care unit admission were included, while those with intensive care unit stays <24 hours or missing key laboratory data were excluded. The SII was calculated using the formula: (platelet count × neutrophil count)/lymphocyte count from initial admission laboratory values. Patients were categorized into tertiles based on their SII values. Kaplan-Meier survival analysis and multivariable Cox proportional hazards models were used to assess the association between SII and 28-day mortality, adjusting for demographic, clinical, and laboratory covariates. A total of 5482 patients were included. Kaplan-Meier analysis showed significant differences in 28-day mortality across SII tertiles (log-rank P < .001). In multivariable Cox models, compared with the lowest tertile, the middle and highest SII tertiles were associated with higher 28-day mortality (hazard ratio = 1.485, 95% confidence interval: 1.193-1.849 and hazard ratio = 2.497, 95% confidence interval: 2.060-3.028; both P < .01). Similar associations were observed for 90-, 180-, and 365-day mortality. Restricted cubic spline analyses suggested a dose-response relationship between SII and 28-day mortality. In addition, adding SII to Acute Physiology Score III and Sequential Organ Failure Assessment improved discrimination for 28-day mortality in receiver operating characteristic analyses. Elevated SII is an independent predictor of increased 28-day all-cause mortality in AHF patients. As a readily available and cost-effective marker, SII could be integrated into early risk stratification protocols to guide personalized therapeutic strategies in acute care settings.