Evaluation of the diagnostic utility of a whole-blood interferon-γ assay for determining the risk of exposure to Mycobacterium tuberculosis in Bacille Calmette-Guerin (BCG)-vaccinated individuals

We evaluated the utility of the "QuantiFERON®-TB Gold In-Tube" (QuantiFERON®) test that uses tuberculosis (TB)-specific antigens for the diagnosis of latent infection in such individuals. We also examined the correlation between the interferon (IFN)-γ response to these antigens and the exposure risk to TB by evaluating antigen-specific IFN-γ release in comparison with IFN-γ release in response to purified protein derivative (PPD) in 3 groups: medical students, nurses in a TB hospital, and TB patients. All nurses and TB patients responded to PPD, whereas 52% (P < 0.0001) and 79.2% (P = 0.04) responded to QuantiFERON®, respectively. In the medical students, only 10.4% responded to QuantiFERON®, whereas 85.2% were positive to PPD (P < 0.0001). There was also a significant correlation between the levels of IFN-γ production and the duration of employment in the group of nurses at the TB hospital, suggesting ongoing exposure in this high-risk group. Thus, these results demonstrate that Mycobacterium tuberculosis-specific IFN-γ release assay accurately discriminates low- and high-risk healthy subjects and might therefore be a useful diagnostic tool for the diagnosis of latent infection in Bacille Calmette-Guerin (BCG)-vaccinated individuals.