Red blood cell distribution width and systemic immune-inflammation index in older adults with sepsis: Associations with in-hospital mortality.

The prognostic value of red blood cell distribution width (RDW) and the systemic immune-inflammation index (SII) in older adults with sepsis remains uncertain. We evaluated their associations with mortality and incremental value beyond clinical predictors. This single-center retrospective cohort study included patients aged ≥65 years admitted to the intensive care unit (ICU) with sepsis between January 2020 and December 2025. RDW and SII were assessed within 24 hours of admission. In-hospital mortality was the primary outcome, and ICU mortality was the secondary outcome. Receiver operating characteristic analysis and multivariable logistic regression assessed discrimination, adjusted associations, and incremental model fit. Among 261 patients (mean age, 79.8 ± 8.9 years), in-hospital and ICU mortality were 62.1% and 55.6%, respectively. RDW was higher in non-survivors and showed weak-to-modest discrimination for in-hospital mortality, with an area under the curve (AUC) of 0.600 and a 95% confidence interval (CI) of 0.538-0.660; findings were similar for ICU mortality (AUC, 0.606; 95% CI, 0.543-0.665). SII showed no significant discrimination. Neither biomarker was independently associated with either outcome after adjustment, and adding both to clinical models did not significantly improve model fit (p = 0.289 and p = 0.089, respectively). Acute Physiology and Chronic Health Evaluation II (APACHE II) score and septic shock remained independently associated with both outcomes. These findings suggest limited incremental prognostic value of admission RDW and SII beyond established clinical predictors in geriatric sepsis.