CALLY Index and Inflammatory Parameters for Predicting Focal Involvement in Human Brucellosis: A Retrospective Cohort Study

Background: Focal involvement in brucellosis complicates clinical management and increases treatment failure risk. This study evaluated the predictive value of routine inflammatory markers and, for the first time, the C-reactive protein-albumin-lymphocyte (CALLY) index for predicting focal complications. Methods: A retrospective cohort study conducted between February 2016 and January 2026 included 203 brucellosis patients, categorized into “no focal involvement” (n = 114) and “focal involvement” (n = 89) groups. Admission blood count parameters, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and CALLY index were compared using Receiver Operating Characteristic (ROC) curves, DeLong tests, and multivariate logistic regression models incorporating CRP, albumin, CALLY index, ESR, hemoglobin, MPV, age, and gender. Results: Patients with focal involvement were older (p = 0.029) and exhibited higher ESR, CRP, neutrophil-to-lymphocyte, and platelet-to-lymphocyte ratios but lower hemoglobin, mean platelet volume, albumin, and CALLY index (p < 0.001). ROC analysis showed ESR had the highest predictive value (AUC: 0.839), followed by albumin (AUC: 0.751) and the CALLY index (AUC: 0.728). DeLong tests confirmed ESR’s statistical superiority over the CALLY index (p = 0.002) and albumin (p = 0.016). In multivariate regression, ESR remained a robust independent prognostic factor (OR: 1.042, p < 0.001), whereas the CALLY index lacked independent significance. Conclusions: Despite its theoretical appeal as a novel immuno-nutritional biomarker, the CALLY index does not outperform traditional markers in predicting focal complications of brucellosis at initial presentation. ESR remains a robust, inexpensive, and statistically superior independent predictor. These findings emphasize that clinicians should continue to rely on widely accessible traditional markers like ESR for early diagnostic risk stratification, while the potential utility of composite scores like the CALLY index may be better reserved for monitoring dynamic therapeutic responses and managing chronic cases.