Diagnostic value of ex vivo pleural fluid interferon-gamma versus adapted whole-blood quantiferon-TB gold in tube assays in tuberculous pleural effusion

ABSTRACT

Noninvasive diagnosis of pleural tuberculosis [TB] remains a challenge due to the paucibacillary nature of the disease. As Mycobacterium tuberculosis [MTB]-specific T cells are recruited into pleural space in TB effusion; their indirect detection may provide useful clinical information. Evaluation of pleural fluid interferon [INF]-gamma levels vs Quantiferon -TB Gold In tube assay [QFT- IT] in blood and its adapted variants, using pleural fluid or isolated pleural fluid cells in the diagnosis of pleural TB. Thirty-eight patients with pleural effusion of unknown etiology presented at Assiut University Hospital, Egypt, were recruited. Blood and pleural fluid were collected at presentation for INF-gamma assays. Ex vivo pleural fluid INF-gamma levels, QFT-IT in blood and its adapted variants were compared with final diagnosis as confirmed by other tools including blind and/or thoracoscopic pleural biopsy. The final clinical diagnosis was TB in 20 [53%], malignancy in 10 [26%], and effusion due to other causes in eight patients [21%]. Ex vivo pleural fluid INF-gamma levels accurately identified TB in all patients and were superior to the QFT-IT assays using blood or pleural fluid [70 and 78% sensitivity, with 60 and 83% specificity, respectively]. QFT-IT assay applied to isolated pleural fluid cells had 100% sensitivity and 72% specificity. The optimal cut-off obtained with ROC analysis was 0.73 for TB Gold assay in blood assay, 0.82 IU/ml for the cultured pleural fluid assay, and 0.94 for isolated pleural cells assay. The ex vivo pleural fluid INF-gamma level is an accurate marker for the diagnosis of pleural TB. QFT- IT assay in peripheral blood or its adapted versions of the assay using pleural fluid and/or washed pleural fluid cells had no diagnostic advantage over pleural fluid INF-gamma in the diagnosis of pleural TB