Systemic Immune-Inflammation Index (SII) as a Predictor of Short-Term Mortality Risk in Sepsis-Associated Acute Kidney Injury: A Retrospective Cohort Study

Background: Sepsis-associated acute kidney injury (SA-AKI) is linked to high mortality rates and an unfavorable prognosis. Early identification of patients with poor prognosis is crucial. This study aimed to investigate the relationship between the systemic immune-inflammation index (SII) and mortality in this specific patient population. Material/Methods: This retrospective cohort study used data from the Medical Information Mart for Intensive Care IV database. ney injury staging, and renal replacement therapy were collected within 48 h of intensive care unit admission. Restricted cubic splines, Kaplan-Meier curves, and Cox regression models were used for analysis. Stratified analyses were performed on the basis of various factors. Results: In total, 7856 patients were included, with a median age of 66.9 years and a male-to-female ratio of 57.7%-42.3%. A J-shaped relationship was observed between SII and mortality risk. The lowest mortality risk occurred at an SII of 760.078x109/L. Compared to the reference group (second quartile of SII), the highest and third quartiles had increased 28-day mortality risk, with adjusted hazard ratios (HRs) of 1.33 (1.16-1.52) and 1.55 (1.36-1.77), respectively. Although a trend towards higher mortality hazard was observed in the lowest SII group (Q1), it was not statistically significant, with an adjusted HR of 1.15 (1-1.32). Conclusions: In patients with SA-AKI, both low and high SII were associated with increased short-term mortality risk. The lowest mortality risk was observed at an SII of 760.078x109/L within a 28-day period.