Risk Stratification in Acute Coronary Syndromes: The Systemic Immune-Inflammation Index as Prognostic Marker

Inflammation plays a key role in acute coronary syndromes (ACS). The systemic immune-inflammation index (SII), which integrates immune and inflammatory markers, may serve as a valuable prognostic tool. This study aimed to evaluate the utility of SII as a short-term predictor of mortality and major adverse cardiovascular and cerebral events (MACCE) in ACS patients.

A retrospective analysis was conducted on 964 ACS patients admitted in 2023. SII was calculated from admission hematological parameters. Primary and secondary outcomes were 30-day mortality and MACCE, respectively.

SII levels differed significantly across ACS subtypes (p < 0.001), highest in ST-segment elevation myocardial infarction (STEMI) and lowest in unstable angina. SII was markedly higher in deceased patients (2003.79 ± 1601.17) vs. survivors (722.04 ± 837.25; p < 0.001) and remained an independent predictor of mortality (OR = 1.038, p < 0.001). Similarly, SII was elevated in MACCE cases (1717 ± 1611.32) vs. non-MACCE (664.68 ± 713.11; p < 0.001) and remained predictive in multivariate analysis (OR = 1.080, p < 0.001). Predictive accuracy for MACCE was moderate (AUC = 0.762), improved when combined with GRACE 2, especially in specificity (p = 0.07). In STEMI, SII had excellent accuracy (AUC = 0.874), outperforming neutrophil-lymphocyte ratio and C-reactive protein. SII rose at 24 h and declined at 48 h in STEMI, with a slower decline in MACCE patients.

SII proved to be a cost-effective biomarker reflecting inflammation, immunity, and thrombosis. Elevated SII predicted short-term MACCE and mortality in ACS, with improved prognostic power when combined with GRACE 2. Persistent elevation may signal ongoing inflammation and increased MACCE risk.