Procalcitonin as a diagnostic marker in differentiating parapneumonic effusion from tuberculous pleurisy or malignant effusion

Objectives: Differential diagnosis of exudative pleural effusions can be difficult, despite the use of several biomarkers. Serum procalcitonin (s-PCT) is a well-known biomarker for systemic bacterial infections. However, the usefulness of pleural fluid procalcitonin (pf-PCT) in clinical practice has not been established. This study evaluated the usefulness of PCT measurements in differentiating parapneumonic effusion (PPE) from tuberculous (TB) pleurisy or malignant effusion. Design and methods: Ninety eight adult patients diagnosed with exudative pleural effusion were enrolled and allocated into the PPE group ( n= 32), TB pleurisy group ( n= 40), or malignant effusion group ( n= 26). Both s-PCT and pf-PCT concentrations were measured at admission using an immunoluminometric assay. Results: Both s-PCT and pf-PCT were significantly increased in the PPE group compared with the TB pleurisy or malignant effusion groups ( p < 0.001). The optimal cut-off value for s-PCT in the diagnosis of PPE was 0.18. ng/mL (sensitivity 83.3%, specificity 81.0%). The pf-PCT cut-off value was 0.16. ng/mL (sensitivity 81.5%, specificity 72.1%). Serum PCT exhibited better diagnostic accuracy than pf-PCT, with areas under the receiver operating characteristic curves of 0.842 for s-PCT and 0.784 for pf-PCT ( p= 0.015). In addition, s-PCT and pf-PCT showed better diagnostic accuracy than serum C-reactive protein ( p= 0.005 and p= 0.023, respectively). Conclusions: Measurement of s-PCT and pf-PCT is useful in differentiating PPE from TB pleurisy and malignant effusion. Both s-PCT and pf-PCT may be useful biomarkers in the differential diagnosis of exudative pleural effusions.