Prognostic value of sCD163, IL-6, PLR, and SII in predicting disease severity in Crimean–Congo hemorrhagic fever: a prospective study

Crimean - Congo hemorrhagic fever (CCHF) is a severe tick-borne infection with high mortality, where macrophage activation and systemic inflammation drive pathogenesis. Prognostic biomarkers are crucial for early risk stratification. In this prospective study (April - July 2025), 60 confirmed CCHF patients (30 severe, 30 mild - moderate) and 50 healthy controls were enrolled. Soluble CD163 (sCD163) and interleukin-6 (IL-6) were measured by ELISA, while platelet-to-lymphocyte ratio (PLR) and systemic immune - inflammation index (SII) were derived from blood counts. Severe cases showed lower platelet counts, PLR, and SII, but higher AST, ALT, LDH, GGT, CK, direct bilirubin, fibrinogen, sCD163, and IL-6 than mild - moderate patients (all <i>p</i> < 0.05). Compared with controls, CCHF patients had elevated sCD163 and IL-6 (<i>p</i> < 0.001). sCD163 correlated negatively with platelet count (<i>r</i>=-0.453, <i>p</i> = 0.001) and positively with AST, ALT, and IL-6 (<i>r</i> = 0.953, <i>p</i> < 0.001), linking macrophage activation to systemic inflammation. ROC analysis showed sCD163 (AUC = 0.853) and IL-6 (AUC = 0.852) as accurate predictors of severe CCHF, with an sCD163 cutoff of 2.7 ng/mL yielding 96% sensitivity and 77% specificity. PLR and SII also distinguished severity but with lower accuracy. These findings highlight sCD163 and IL-6 as strong early prognostic biomarkers that may improve clinical assessment and guide timely therapeutic interventions in CCHF.