Evaluation of QuantiFERON-TB Gold Plus for Detection of Mycobacterium tuberculosis infection in Japan

Performance of interferon-γ (IFN-γ) release assays still needs to be improved. The data on the performance of QuantiFERON-TB Gold Plus (QFT-Plus), a new-generation of QFT assay are limited. This study evaluated the diagnostic performance of QFT-Plus, and compared to that of QuantiFERON-TB Gold In-Tube (QFT-GIT). Blood samples were collected from 162 bacteriologically confirmed tuberculosis (TB) patients and 212 Mycobacterium tuberculosis-uninfected volunteers; these samples were then tested with QFT-GIT and QFT-Plus. The IFN-γ concentration of QFT-Plus was lower than that of QFT-GIT in TB patients (p < 0.001). Receiver operating characteristic curves were compared between QFT-GIT and QFT-Plus. Both assays showed area under the curve values over 0.99 without significant difference. Using the conventional cut-off (0.35 IU/mL) for QFT-GIT, QFT-Plus had a lower sensitivity of 91.1% compared to 96.2% (p = 0.008) at its optimum cut-off (0.168 IU/mL) with the same specificity. Moreover, IFN-γ values were significantly reduced with age in QFT-GIT (p = 0.035) but not in QFT-Plus. The diagnostic performance of QFT-Plus was as accurate as that of QFT-GIT despite a lack of TB7.7 antigen and despite the decrease in quantitative values. However, the cut-off value for QFT-Plus should be considered independently from that of QFT-GIT to obtain the best sensitivity without compromising specificity.