Role of the quantiferon-TB test in ruling out pleural tuberculosis: a multi-centre study.

Diagnosing pleural tuberculosis (plTB) might be difficult due to limited sensitivity of conventional microbiology tools. As M. tuberculosis (MTB)-specific T cells are recruited into pleural space in plTB, their detection may provide useful clinical information. To this aim, in addition to standard diagnostic tests, we used the QuantiFERON-TB Gold In-Tube (QFT-IT) test in blood and pleural effusion (PE) samples from 48 patients with clinical suspicion of plTB, 18 (37.5\%) of whom had confirmed plTB. Four of them (22.2\%) tested positive with a nucleic acid amplification test for MTB. The tuberculin skin test was positive in most confirmed plTB cases (88.9\%). Positive QFT-IT tests were significantly more frequent in patients with confirmed plTB, as compared to patients with an alternative diagnosis, both in blood (77.7 vs 36.6\%, p=0.006) and in PE samples (83.3\% vs 46.6\%, p=0.02). In addition, both blood and PE MTB-stimulated IFN-gamma levels were significantly higher in plTB patients (p=0.03 and p=0.0049 vs non-plTB, respectively). In blood samples, QFT-IT had 77.8\% sensitivity and 63.3\% specificity, resulting in 56.0\% positive (PPV) and 82.6\% negative (NPV) predictive values. On PE, QFT-IT sensitivity was 83.3\% and specificity 53.3\% (PPV 51.7\% and NPV 84.2\%). The optimal AUC-derived cut-off for MTB-stimulated pleural IFN-gamma level was 3.01 IU/mL (77.8\% sensitivity, 80\% specificity, PPV 68.4\% and NPV 82.8\%). These data suggest that QFT-IT might have a role in ruling out plTB in clinical practice.