The Predictive Ability of the Aggregate Index of Systemic Inflammation for Complicated Acute Appendicitis

To evaluate the predictive ability of the Aggregate Index of Systemic Inflammation (AISI) for complicated acute appendicitis in adult patients presenting to the emergency department. A retrospective diagnostic validity study was conducted including 546 adults diagnosed with acute appendicitis between March 2020 and October 2022. Complicated appendicitis was defined as perforation, gangrenous changes, or abscess formation. Hematologic parameters, including AISI calculated as (Neutrophils × Monocytes × Platelets)/Lymphocytes, were assessed. Receiver operating characteristic (ROC) analysis determined discriminative ability, and multivariate logistic regression identified independent predictors. Of 546 patients, 137 (25.1%) had complicated appendicitis. AISI was significantly associated with complicated appendicitis in multivariate analysis (OR 1.043; 95% CI 1.013–1.074; p = 0.044), but its discriminative ability was limited (AUC: 0.565; sensitivity 46%, specificity 66%). C-reactive protein was the strongest independent laboratory predictor (OR 1.016; 95% CI 1.011–1.022; p < 0.001). Other hematologic parameters demonstrated similarly low predictive performance. The negative predictive value of AISI was high (78.5%), suggesting potential utility in ruling out complicated cases. Although AISI alone has limited discriminative ability for diagnosing complicated acute appendicitis, it is an independent predictor with a high negative predictive value. Its simplicity, low cost, and accessibility may make it a practical adjunctive tool, particularly in resource-limited settings. Integration with clinical, laboratory, or imaging findings could enhance diagnostic accuracy.