Association between serum ferritin and mortality in patients with severe fever with thrombocytopenia syndrome: A retrospective cohort study

The role of serum ferritin, an acute-phase inflammatory marker, in predicting mortality in patients with severe fever with thrombocytopenia syndrome (SFTS) is not fully understood. This study aimed to investigate the association between serum ferritin levels and inpatient mortality in patients with SFTS. We conducted a retrospective analysis using data from patients diagnosed with SFTS at the Second Affiliated Hospital of Anhui Medical University between May 2017 and September 2024. The association between serum ferritin levels and in-hospital mortality in patients with SFTS was assessed using Cox regression models and restricted cubic spline (RCS) analysis. The receiver operating characteristic (ROC) curve was used to determine the optimal serum ferritin cut-off value for predicting mortality risk. Kaplan–Meier survival curves were compared for survival rates, and propensity score matching with linear trend testing was applied to ensure robustness. This study included 390 patients with SFTS, of whom 312 survived and 78 did not, yielding an in-hospital mortality rate of 20.0%. Cox regression and RCS analyses demonstrated a significant linear association between higher serum ferritin levels and increased in-hospital mortality in patients with SFTS, indicating that the predicted mortality of patients with SFTS increased with elevated serum ferritin levels beyond a certain threshold. ROC analysis revealed an area under the curve of 0.830, with an optimal serum ferritin cut-off of 3.975 (lg, ng/ml), sensitivity of 0.731, and specificity of 0.830. Clinically, serum ferritin levels above 4 (lg ng/ml), were associated with a substantial increase in mortality risk. Sensitivity analysis supported the robustness of these results. Serum ferritin levels are linearly associated with mortality risk in patients with SFTS, with mortality significantly increasing when serum ferritin levels exceed 10,000 ng/ml. Serum ferritin level may serve as a valuable prognostic biomarker for mortality risk in patients with SFTS.