Systemic Inflammatory Indices (SII and SIRI) in 30-Day Mortality Risk Stratification for Community-Acquired Pneumonia: A Study Alongside CURB-65 and PSI

Community-acquired pneumonia (CAP) remains a leading cause of morbidity and mortality worldwide, underscoring the need for accessible and cost-effective biomarkers to support early risk assessment. This retrospective study investigated the prognostic performance of two systemic inflammatory indices-the Systemic Immune-Inflammation Index (SII) and the Systemic Inflammation Response Index (SIRI)-in 240 adults hospitalized with CAP between January and December 2024. The primary outcome was 30-day all-cause mortality. Logistic regression and receiver operating characteristic (ROC) analyses were applied to compare these indices with established severity scores, CURB-65 and the Pneumonia Severity Index (PSI). Thirty-day mortality occurred in 15.4% of patients. Non-survivors exhibited significantly higher SII values (<i>p</i> = 0.043) and a trend toward increased SIRI levels (<i>p</i> = 0.072). Both indices showed weak but statistically significant positive correlations with conventional inflammatory markers such as C-reactive protein and procalcitonin. While CURB-65 and PSI retained superior discriminative ability, SII and SIRI provided only modest prognostic information and did not significantly improve mortality prediction beyond these scores. These findings indicate that simple, hematology-based indices reflecting systemic inflammation may offer limited but potentially clinically relevant adjunctive information when integrated with traditional clinical scoring systems.