Procalcitonin—A Useful Biomarker for Pneumonia Associated with <i>Rhodococcus equi</i>?

Background: Procalcitonin, a precursor protein of the hormone calcitonin, is a sensitive marker for sepsis in human medicine, which is used for diagnosis of bacterial pneumonia in adults and neonates to initiate antibiotic therapy. Objectives: In this study, procalcitonin was evaluated as a potential biomarker for Rhodococcus equi associated pneumonia. Methods: In four foals procalcitonin was measured at four time-points (day 0 before antibiotic therapy, day 1, 3 and 5/6 during therapy) in plasma using an equine specific ELISA. Inclusion criteria for the study were a positive sepsis score, ultrasonographic evidence of pulmonary abscesses in addition >8 cm, a positive microbiology out of tracheobronchial secretion and positive response to antibiotic treatment (azithromycin 10 mg/kg BDW 24q PO and rifampicin 10 mg/kg BDW 12q PO) within a weak including improvement of clinical status and reduction of ultrasonographic score <8 cm. Results: Procalcitonin concentrations remained below the working range of the ELISA (25 - 1000 ng/ml) in all but one sample. Conclusions: Procalcitonin cannot be regarded a useful biomarker in pneumonia associated with Rhodococcus equi.