Prediction of In-Hospital Mortality in Patients with NSTEMI Using Systemic Immune-Inflammation Index and Systemic Inflammatory Response Index: A Retrospective Prognostic Study

This study aimed to compare the prognostic performance of the Systemic Immune-Inflammation Index (SII) and the Systemic Inflammatory Response Index (SIRI) for predicting in-hospital mortality in patients with non-ST-elevation myocardial infarction (NSTEMI). This retrospective observational study included 157 patients with NSTEMI admitted to a tertiary emergency department between October 1, 2022, and October 1, 2023. Demographic characteristics, laboratory findings, and clinical outcomes were retrieved from hospital records. SII and SIRI were calculated using hematological parameters obtained from blood samples collected at emergency department admission. Patients were divided into two groups according to the occurrence of in-hospital mortality. Group comparisons were performed using appropriate statistical tests, and multivariable logistic regression analyses were used to identify independent predictors. Receiver operating characteristic (ROC) curve analysis was performed to evaluate prognostic performance. In-hospital mortality occurred in 15 patients (9.6%). Patients in the mortality group had significantly higher SII (p = 0.002), SIRI (p < 0.001), age, and C-reactive protein levels. In ROC analysis, the area under the curve was 0.748 (95% confidence interval [CI]: 0.627–0.870) for SII and 0.804 (95% CI: 0.680–0.927) for SIRI. In multivariable analysis, only SII remained independently associated with in-hospital mortality (odds ratio: 1.001; 95% CI: 1.000–1.002; p = 0.041), whereas SIRI was not statistically significant in the adjusted model. SII was associated with in-hospital mortality in patients with NSTEMI and may have potential value as a supportive prognostic biomarker. However, given the retrospective single-center design and limited number of outcome events, these findings should be interpreted with caution and considered hypothesis-generating. Further validation in larger prospective multicenter studies is warranted.