Procalcitonin in pleural fluid: A new tool for the diagnosis of empyema and parapneumonic pleural effusions?

Background: Few data are available about the usefulness of procalcitonin (PCT) measurement in pleural effusions. Results are controversial with 3 studies with negative results and 2 with promising results in parapneumonic pleural effusions. No study has assessed the value of PCT in pleural liquid. Methods: We conducted a study to assess the reliability and the reproducibility of PCT measurements in pleural fluid and to determinate its performance for the diagnosis of parapneumonic pleural effusions through ROC curves. Results: We measured PCT in the pleural liquid of 35 patients (550 mesures) with pleural effusion (3 transudates in acute heart failure, 13 metastatic pleural effusion, 17 empyema and parapneumonic effusion and 2 exudates due to an other cause). PCT values were low in 16 cases (< 0.18 ng/ml), medium in 10 cases (between 0.18 and 1 ng/ml) and high in 9 cases (> 1 ng/ml). Reliability: thirty consecutive measurements of the same sample showed a low variation coefficient (< 4%) for medium and high PCT values. A similar variation coefficient was found when PCT was tested in blood. Reproducibility: samples were also kept at 4°C and were tested every day during 5 days with a variation coefficient less than 5% for medium and high PCT values, and less than 4% for the first 3 days. For the diagnosis of empyema or parapneumonic pleural effusions, the ROC curve determined a 0.183 ng/ml PCT cut-off, with a 80% sensitivity and specificity. Conclusion: PCT could be considered as a useful tool in diagnosis of empyema and parapneumonic pleural effusion with a 80% sensitivity and specificity for a 0.183 ng/ml cut-off. Furthers studies are required to confirm these data.