Abstract
Objective: This study aimed to evaluate the discriminatory performance of the C-reactive protein–albumin–lymphocyte (CALLY) index in complicated acute appendicitis and compare it with C-reactive protein (CRP) alone and other inflammatory indices. Materials and Methods: This single-center retrospective study included adults diagnosed with acute appendicitis between January 2021 and December 2025. Diagnostic performance was assessed using receiver operating characteristic analysis, with paired DeLong tests for AUC comparisons. Separate logistic regression models were adjusted for age and sex, and internal validation was performed using 350 bootstrap resamples. Results: Of 1733 patients screened, 1634 were included, of whom 306 (18.7%) had complicated appendicitis. CALLY and CAR each achieved an AUC of 0.782, compared with 0.778 for CRP alone. CALLY did not significantly outperform CAR (p = 0.913) or CRP (p = 0.489). Although CAR showed statistically higher discrimination than CRP (p = 0.006), the absolute AUC difference was small. CALLY demonstrated higher discrimination than HALP, SII, and PIV (all p < 0.001). In age- and sex-adjusted analysis, each doubling of CALLY was associated with lower odds of complicated appendicitis (adjusted odds ratio, 0.623; 95% CI, 0.580–0.670). The optimism-corrected AUC of the CALLY-extended model was 0.795. Conclusions: CALLY showed moderate discrimination of complicated acute appendicitis but no demonstrated advantage over CAR. Whether CALLY adds value beyond simpler laboratory measures requires further evaluation and external validation.