# Procalcitonin/albumin to urea nitrogen ratio: a novel prognostic indicator for severe fever with thrombocytopenia syndrome

## TL;DR

This study identifies a new blood test (PAU ratio) that can predict survival in patients with a severe tick-borne disease called SFTS.

## Contribution

The study introduces the procalcitonin/albumin to urea nitrogen ratio (PAU) as a novel prognostic biomarker for SFTS.

## Key findings

- PAU was an independent predictor of adverse outcomes in SFTS patients with strong discriminative performance (AUC 0.810).
- Combining PAU with age, viral load, and altered mental status improved predictive accuracy (AUC 0.897).
- High PAU levels correlated with worse prognosis and distinct longitudinal trends in non-survivors versus survivors.

## Abstract

Severe fever with thrombocytopenia syndrome (SFTS), caused by the novel Bunyavirus (NBV), is a tick-borne infectious disease associated with high morbidity and mortality. Currently, no effective treatment or vaccine exists for SFTS. Early identification of prognostic factors is crucial for clinical management. This study aimed to evaluate the prognostic value of the procalcitonin/albumin to urea nitrogen ratio (PAU) in SFTS patients.

This retrospective observational study enrolled 259 consecutive patients with SFTS admitted to Tongji Hospital from April 2023 to November 2024. Patients were stratified into survival (n = 172) and death (n = 87) groups based on clinical outcomes.

Multivariable logistic regression identified advanced age, altered mental status (AMS), elevated PAU and high viral load as independent predictors of adverse outcome in SFTS. PAU exhibited strong discriminative performance (AUC 0.810; 95% CI 0.757–0.857; sensitivity 75.7%, specificity 73.0%), with an optimal cut-off of 0.06 µmol/L. Integration of PAU with age, viral load and AMS further improved accuracy (AUC 0.897; 95% CI 0.858–0.936). Bootstrap internal validation yielded a calibration curve closely approximating the diagonal, confirming robust predictive efficacy of the composite model.Kaplan-Meier analysis revealed significantly worse prognosis in high-PAU patients (P < 0.001).The longitudinal trend analysis revealed an increasing trend in PAU among non-survivors, while survivors exhibited a decreasing trend.

PAU represents a novel composite biomarker that integrates inflammatory and organ dysfunction parameters, providing reliable prognostic prediction for SFTS patients.

Not applicable.

The online version contains supplementary material available at 10.1186/s12879-026-12736-6.