Evaluation of hematological and biochemical parameters in the differential diagnosis of Crimean-Congo hemorrhagic fever and brucellosis: insights from a large patient cohort.

backgroundIn Türkiye, where both Crimean-Congo Hemorrhagic Fever (CCHF) and brucellosis are endemic, these infections share common presenting symptoms, including fever and musculoskeletal complaints, as well as overlapping laboratory findings such as thrombocytopenia and elevated liver enzymes, making early differential diagnosis challenging. Given their distinct infection control and management requirements, this study aimed to evaluate the diagnostic performance of routine hematological and biochemical parameters for differentiating these infections before confirmatory test results become available.

methodsIn this retrospective study, a total of 1,578 patients [1,171 (74.2%) with CCHF and 407 (25.8%) with brucellosis] followed at two tertiary care centers between January 1, 2015 and January 1, 2025 were analyzed. Demographic, clinical, and laboratory parameters were compared. Receiver operating characteristic (ROC) curve analysis was performed, and area under the curve (AUC) values were calculated. Optimal cut-off values were determined using the Youden index. Multivariable logistic regression analysis was subsequently conducted to identify independent predictors differentiating CCHF from brucellosis.

resultsWhite blood cell count (WBC), lymphocyte count, monocyte count, and platelet count demonstrated significant discriminatory performance for differentiating CCHF from brucellosis. The highest diagnostic performance was observed for lymphocyte count (AUC: 0.933; cut-off ≤ 1.09 × 10⁹/L, sensitivity 91%, specificity 83%) and platelet count (AUC: 0.927; cut-off ≤ 151 × 10⁹/L, sensitivity 89%, specificity 85%). Monocyte count (AUC: 0.888; cut-off ≤ 0.35 × 10⁹/L, sensitivity 81%, specificity 83%) and WBC (AUC: 0.880; cut-off ≤ 4.47 × 10⁹/L, sensitivity 89%, specificity 79%) also demonstrated high discriminatory ability. Among biochemical parameters, ferritin (AUC: 0.845) and creatine kinase (CK) (AUC: 0.826) showed the highest diagnostic performance. Multivariable logistic regression analysis identified lower lymphocyte count (OR = 0.601, 95% CI = 0.464-0.778, p < 0.001), lower platelet count (OR = 0.978, 95% CI = 0.972-0.985, p < 0.001), and elevated CK levels (OR = 1.003, 95% CI = 1.001-1.005, p = 0.005) as independent predictors of CCHF.

conclusionsFindings from this large cohort demonstrate that routine hematological and biochemical parameters exhibit strong discriminatory performance in differentiating between CCHF and brucellosis. In particular, lymphocyte counts, platelet counts, and CK levels-which were identified as independent predictors favoring CCHF-may serve as valuable adjuncts to clinical evaluation, thereby facilitating the prioritization of confirmatory serological and molecular testing during the early diagnostic phase.