Dynamic Prognostic Value of IL‐6/PLT Ratio for Mortality Discrimination in Patients with Crimean‐Congo Hemorrhagic Fever: Sequential ROC Analysis Throughout the Clinical Course

ABSTRACT This study aimed to compare the prognostic performances of individual laboratory parameters and biomarker ratios derived from them formortality in patients with Crimean‐Congo Hemorrhagic Fever (CCHF), and to examine the temporal stability of the strongest index. A total of 1171 adult patients with laboratory‐confirmed CCHF followed between 2014 and 2024 were retrospectively included in the study. Admission data were recorded, and the mortality discriminative performances of individual and derived biomarkers (interleukin‐6‐to‐platelet ratio [IL‐6/PLT], interleukin‐6‐to‐calcium ratio [IL‐6/Ca], ferritin‐to‐platelet ratio [Ferritin/PLT], and ferritin‐to‐calcium ratio [Ferritin/Ca]) for mortality were compared using ROC analysis. Ninety‐seven patients (8.3%) resulted in mortality. Among the individual parameters, IL‐6 demonstrated the highest discriminative ability for mortality (AUC: 0.887). Among the derived indices, the IL‐6/PLT ratio demonstrated the highest overall performance with an AUC value of 0.920 (95% CI: 0.871–0.969; p < 0.001). The optimal cut‐off value for the IL‐6/PLT ratio was determined as 0.78 (88% sensitivity, 81% specificity). Mortality reached 100% in all patients with a ratio of ≥ 16. Sequential ROC analyzes demonstrated that the IL‐6/PLT ratio maintained high prognostic stability throughout the course of infection. The IL‐6/PLT ratio, a combined indicator of inflammatory response and hemostatic dysfunction, is a powerful biomarker candidate for the early and dynamic monitoring of mortality risk in CCHF.