Systemic Inflammation Index (SII) as a Predictor of Mortality in Intensive Care Units

Background: The Systemic Inflammation Index (SII), associated with increased systemic inflammation and adverse outcomes, has been demonstrated to be efficacious and a significant biomarker in different patient populations. This investigation aims to examine the correlation between the admission SII, a relatively new biomarker, and 28-day mortality outcomes in intensive care units (ICUs). Methods: This retrospective cohort analysis was undertaken in a tertiary-level ICU in Turkey from 3 April 2024 through 31 December 2024. Baseline demographic data, clinical characteristics, and laboratory parameters were recorded. Inflammatory parameters such as SII, NLR, and PLR were calculated at the time of ICU admission. SII = neutrophil count (10³/ill) × PLT count (10³/μL)/lymphocyte count, NLR = neutrophil count (10³/μL)/lymphocyte count (10³/μL), and PLR = PLT (10³/μL)/lymphocyte count (10³/μL). Results: In this study, a total of 702 patients who met the eligibility criteria were recruited. The study's overall mortality rate for 28 days was 36.9% with 259 deaths. The median age of the cohort was 70 years (57-80), with 41.6% of the participants being female. The SII was markedly elevated in non-survivors compared to survivors (p = 0.010). The analysis revealed that the SII/1000 was an independent predictor of elevated mortality risk (OR 1.029, 95% CI 1.001-1.057, p = 0.042). Conclusions: The identification of the Systemic Inflammation Index on admission to the ICUs is of critical importance. The SII has been demonstrated to serve as a significant and independent predictor of mortality. There is a need for prospective and large-scale studies to generalize this finding to other populations or for more widespread use in clinical practice.