IntroductionWhether the inflammatory biomarker procalcitonin provides prognostic information across clinical settings and different acute respiratory tract infections (ARI) is poorly understood. Herein, we investigated the prognostic value of admission procalcitonin levels to predict adverse clinical outcome in a large ARI population. Methods: We analysed data from 14 trials and 4211 ARI patients to study associations of admission procalcitonin levels and setting specific treatment failure and mortality alone at 30 days. We used multivariable hierarchical logistic regression and conducted sensitivity analyses stratified by clinical settings and ARI diagnoses to assess the results’ consistency. Results: Overall, 864 patients (20.5%) experienced treatment failure and 252 (6.0%) died. The ...