Diagnostic utility of pleural fluid IFN-gamma in tuberculosis pleural effusion

Pleural fluid interferon-gamma (IFN-gamma) levels are increased in patients with tuberculosis (TB) pleural effusion. Recent studies from the west have found that estimation of pleural fluid IFN-gamma levels is an excellent diagnostic strategy for these patients. The diagnostic utility of pleural effusion IFN-gamma level estimation has not been evaluated in patients from developing countries, however. This work was carried out to study the diagnostic utility of IFN-gamma level estimation in patients with TB pleural effusion and to define the best cutoff of IFN-gamma for diagnosis TB pleural effusion. We studied 101 patients with pleural effusion. Of these, 64 were found to have a TB etiology, established by means of various conventional modalities. Measurement of pleural fluid IFN-gamma levels was done by ELISA technique. The median value of pleural fluid IFN-gamma levels in patients with TB (1480 pg/ml, range 3-14,000 pg/ml) was significantly higher (p < 0.001) compared with the non-TB group (3 pg/ml, range 0-900 pg/ml). The receiver operator characteristic (ROC) curve for IFN-gamma showed an area under the curve (AUC) value of 0.954, and the best cutoff was computed to be 138 pg/ml. Using this cutoff for IFN-gamma levels in pleural fluid for the diagnosis of TB, sensitivity, specificity, negative predictive value, and positive predictive value were found to be 90.2%, 97.3%, 85.7%, and 98.3%, respectively. Estimation of IFN-gamma levels in pleural fluid is a useful diagnostic modality for TB pleural effusion. A cutoff of 138 pg/ml provides the best sensitivity and specificity for diagnosis of TB.