Diagnostic and prognostic values of pleural fluid procalcitonin in parapneumonic pleural effusions

Background: The role of procalcitonin (PCT) in parapneumonic pleural effusion (PPPE) as a diagnostic and prognostic biomarker of the outcome has not been examined before. Methods: From the emergency department, 82 adult patients with pleural effusions were enrolled in this prospective study and divided into the following two groups: the PPPE group (n = 45); and the non-PPPE group (n = 37). Levels of pleural fluid (PF) PCT and serum (S) PCT were determined in all patients after study enrollment as well as on day 3 only in the PPPE group by a newly developed time-resolved, amplified, cryptate emission assay. Results: Both PF-PCT and S-PCT levels were significantly higher in the PPPE group than the non-PPPE group (p = 0.01 and 0.0003, respectively). S-PCT had a better diagnostic performance than PF-PCT, with an area under the curve of the receiver operating characteristic of 0.834 for S-PCT and 0.752 for PF-PCT (p = 0.006). In the PPPE group, both PF-PCT and S-PCT levels on days 1 and 3 were significantly higher in patients who were in high-severity risk classes (all p values < 0.05). Day 3 PF-PCT/S-PCT ratios were significantly lower in patients who needed chest tube drainage for > 7.5 days (corrected p = 0.02). Conclusion: S-PCT has higher diagnostic accuracy than PF-PCT in differentiating PPPEs from non-PPPEs. However, both PF-PCT and S-PCT are useful in the severity assessment of patients with PPPEs. The PF-PCT/S-PCT ratio may help to predict prolonged chest tube drainage.