Characteristics of IFN-γ responses in IGRA among pulmonary TB suspects in a TB-endemic area

Although the diagnostic value of interferon-γ (IFN-γ) release assays for active tuberculosis (TB) is limited, the characteristic of non–TB-specific IFN-γ responses among TB suspects deserves further evaluation. We enrolled clinically suspected pulmonary TB (PTB) patients, and QuantiFERON-TB Gold In-Tube (QFT-GIT) was performed. The characteristics of IFN-γ responses were analyzed. Among 392 patients, active PTB patients had stronger IFN-γ responses to TB antigen (TBAg-Nil, P < 0.001) and lower responses to mitogen (Mitogen-Nil, P < 0.001). Lower body mass index (P = 0.001), without bacille Calmette-Guerin vaccination (P = 0.026), and active PTB (P = 0.011) were independent factors associated with lower non–TB-specific IFN-γ responses. Among TB suspects with higher TBAg-Nil (>1.02 U/mL) and lower Mitogen-Nil (<5.5 U/mL), 84.3% were active PTB cases. Among TB suspects with lower TBAg-Nil and higher Mitogen-Nil, only 4.7% were active PTB. The present study suggested that the possibilities of active PTB should be carefully excluded in TB suspects with stronger TB-specific and lower non–TB-specific IFN-γ responses in QFT-GIT.