RESUMO
Context: Despite recent advances in the available diagnostic modalities, diagnosis of pleural tuberculosis remains a challenge because of the low yield of conventional methods. Pleural biopsy is the gold standard for confirmation of diagnosis, which is invasive and cumbersome. The concentration of mycobacterial peptide-specific activated lymphocytes at the site of infection can be utilized as the basis for using IGRA (interferon-gamma release assays) based evaluation of undiagnosed exudative pleural effusions. Aim: To evaluate the performance of IGRA (Enzyme-linked Immunospot (ELISPOT) in pleural fluid for the diagnosis of pleural tuberculosis in histopathologically confirmed cases. Settings and Design: A prospective observational study compared the utility of ELISPOT with thoracoscopy guided pleural biopsies for the diagnosis of tubercular pleural effusions. Methods and Material: Forty-two consecutive cases of undiagnosed pleural effusions were enrolled and subjected to thoracoscopy guided pleural biopsy. Thirteen patients were confirmed to have tuberculosis, 27 had malignancy, and 2 had normal pleura. A total of 1x103 pleural fluid mononuclear cells (PFMCs) were cultured in the presence of early secretory antigenic target-6 (ESAT-6) and culture filtrate protein-10 (CFP-10) for 24 hours. The individual spots were then counted using an automated analyzer ELISPOT reader system. Results: The number of spots developed in the pleural fluid was significantly higher in tubercular pleural effusions as compared to non-tubercular effusions (CFP-10:154.76±14.61 vs 49.24±8.9; ESAT-6: 150.3±17.27 v/s 45.34±8.23, p<0.001). At a cut-off value of more than 67 spots taken as positive for tuberculosis, the sensitivity of the test was 100% (95% CI 75.29% to 100.00%), specificity was 96.5% (95 % CI 82.24% to 99.91%), positive predictive value was 92.86% (95 % CI 65.45% to 98.89%) and negative predictive value was 100%. Conclusions: ELISPOT can be a useful non-invasive test for the evaluation of undiagnosed pleural effusions and making a diagnosis of pleural tuberculosis with confidence.