Predictive value of systemic immune-inflammatory indices for severe acute cholangitis and in-hospital mortality

Background Acute cholangitis (AC) is a potentially life-threatening biliary infection requiring early identification of patients at risk for severe disease and in-hospital mortality. While several systemic immune-inflammatory indices derived from routine laboratory tests have been proposed as prognostic biomarkers, their head-to-head comparative performance in AC remains unclear. This study aimed to compare the predictive performance of six systemic immune-inflammatory indices for severe AC and in-hospital mortality. Methods This retrospective observational study included consecutive adults with confirmed AC diagnosed according to the Tokyo Guidelines 2018 (TG18) at a tertiary emergency department between January 1, 2020, and December 31, 2024. Neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), systemic immune-inflammation index (SII), systemic inflammation response index (SIRI), aggregate index of systemic inflammation (AISI), and prognostic nutritional index (PNI) were calculated from admission laboratory data. Discriminatory performance was assessed using receiver operating characteristic (ROC) curve analysis. Areas under the curve (AUCs) were compared using the DeLong test with Holm–Bonferroni correction. Logistic regression was used to evaluate associations with severe AC and in-hospital mortality. Final multivariable models were internally validated using 1000 bootstrap resamples. Results A total of 137 patients were included, of whom 37 (27.0%) had severe AC and 17 (12.4%) died during hospitalization. PNI showed the highest discriminatory performance for severe AC (AUC, 0.785) and in-hospital mortality (AUC, 0.861), although it was not significantly superior to the other high-performing indices after multiple-comparison adjustment. In multivariable analyses, PNI and SIRI remained associated with both outcomes. Internal bootstrap validation showed limited apparent optimism in model performance. Conclusions Among the evaluated systemic immune-inflammatory indices, PNI showed the highest discriminatory performance for both severe AC and in-hospital mortality, while PNI and SIRI remained associated with both outcomes. These indices are derived from routinely available admission laboratory parameters and may warrant further evaluation for risk stratification; however, their clinical utility requires further validation.