USE OF PLEURAL FLUID C-REACTIVE PROTEIN LEVEL AS A DIAGNOSTIC MARKER FOR PLEURAL EFFUSIONS

Background: Our objective was to determine the usefulness of pleural effusion C reactive protein levels in the di- agnosis of pleural effusions. Patients and Methods: A comparison of serum and pleural fluid C-reactive protein (CRP) levels in different subgroups of 286 patients with pleural effusion was made. We assessed prospectively the sensitivity, specificity, positive and negative predictive values, accuracy, Youden index, likelihood ratio and ROC curve of the test, for a period from February 2008 to November 2011. Results: Among 286 patients with pleural effusion, 67 patients were included in the transudate group, 219 patients were included in the exudate group. In transudates the cut-off value of pleural fluid CRP ≤15 mg/L had a Youden index of 0.678 and the area under curve = 0.86 comparing with exudative pleural effusions. In malignant pleural effusions, the cut-off value of pleural fluid CRP ≤20mg/L had a Youden index of 0.728 and the area under curve = 0.89 comparing with tuberculous effusions. In tuberculous effusions, the cut-off value of pleural fluid CRP >20mg/L had a Youden index of 0.45 and the area under curve=0.96 comparing with malignant effusions. The values of pleural fluid/blood CRP ratios had a very small Youden index and the area under curve in all subgroups of patients with pleural effusion. Conclusions: Levels of CRP in exudative pleural effusions less than 20 mg/L are strongly suggestive of malignant effusion and chronic tuber - culous effusion.A CRP pleural fluid level > 20mg/L almost excludes transudative pleural effusion while the levels of CRP above 30mg/L are suggestive of an inflammatory etiology and almost exclude malignant pleural effusion.