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: IL-6/PLT Ratio for Mortality Discrimination in CCHF.

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.