Usefulness of the QuantiFERON TB-2G test for the differential diagnosis of pulmonary tuberculosis

Objective We prospectively evaluated the usefulness of the QuantiFERON TB-2G (QFT-2G) compared to that of tuberculin skin test (TST) as a supportive method of diagnosing pulmonary tuberculosis (TB) without invasive examinations. Methods The subjects were 90 patients who required differentiation of pulmonary TB clinically and for whom a definitive diagnosis could not be obtained after admission. The final clinical diagnosis of TB infection in 28 patients and non-TB infection in 62 patients was established using bronchoscopic procedures. Results In patients with TB infection, the positive response rate on QFT-2G (79%) was significantly higher than that on TST (57%). The QFT-2G negative rate (5%) was significantly lower than that on TST (48%) in patients with non-TB infection. For QFT-2G test, there was a positive response in 25 patients, a negative response in 49, and indeterminate findings in 16. Of the two patients with a false-negative result on QFT-2G, one had pulmonary TB during immunosuppressive treatment and one had pulmonary tuberculoma. Of the three non-TB patients with a positive result on QFT-2G, two had pneumonia and one had pulmonary mycosis. Four TB patients with an indeterminate result on QFT-2G included two elderly patients and two immunocompromised patients. Conclusions We could confirm the usefulness of the QFT-2G test compared to TST in patients requiring a differential diagnosis between pulmonary TB and other pulmonary diseases in this series. Therefore, we recommend the QFT-2G test as one of the useful noninvasive diagnostic examinations for pulmonary TB.