Validity of procalcitonin and C-reactive protein measurement when differentiating between benign and malignant pleural effusion.

BACKGROUND: Procalcitonin (PCT) and C-reactive protein (CRP) measurements in pleural fluid and plasma have been proposed to facilitate differential diagnosis of pleural effusion (PE). The primary aim of this study was to evaluate the usefulness of these measurements when differentiating between benign (BPE) and malignant pleural effusion (MPE). METHODS: We prospectively studied 100 patients with the specific diagnosis of exudative PE. We analyzed the demographic data and the usual biochemical studies in PE. CRP and PCT were measured in pleural fluid and plasma before starting treatment. RESULTS: The CRP levels in pleural fluid were higher in patients with BPE than in patients with MPE [33.1 mg/L (16.8 to 52.1) vs. 11.8 (5.1 to 22); p = 0.001], as were the plasma CRP levels [68.4 mg/L (26.1 to 119.1) vs. 30.2 (11.7 to 64.8); p = 0.007]. No differences in PCT levels were detected between the two patient populations. The AUC derived from the ROC curve analysis for plasma CRP and pleural fluid CRP were 0.667 (CI 95%: 0.551 - 0.782) and 0.752 (CI 95%: 0.653 - 0.852), respectively. Plasma CRP levels > or = 35.5 mg/L exhibited 71% sensitivity and 56% specificity in discriminating between BPE and MPE. Pleural fluid CRP levels > or = 16.7 mg/L had 75% sensitivity and 68% specificity in the diagnosis of BPE. CONCLUSIONS: CRP levels in the pleural fluid and plasma were higher in patients with BPE, particulary infectious PE. However, the measurement of CRP and PCT is not a useful parameter for discriminating between BPE and MPE and does not provide useful information in clinical practice.