[QFT test and TST test in diagnosis of TB infection]

At present, there are only two methods to diagnose tuberculosis infection in the world, tuberculin skin test (TST) and interferon gamma release assays (IGRAs). Since TST could show positive responses due to BCG vaccination or infection of non-tuberculous mycobacterium and BCG vaccination is widely done in Japan, TST has a critical problem in its specificity. QuantiFERON-TB Gold (QFT-G/QFT-3G) is one of IGRAs and uses M. tuberculosis-specific antigens (ESAT-6, CFP-10, TB7.7) for stimulation of whole blood to induce IFN-gamma production by antigen-specific T cells. Produced IFN-gamma is measured by ELISA system. IFN-gamma is produced by individuals with TB infection but not by BCG-vaccinated individuals without TB infection. As QFT can detect TB infection among BCG vaccinated individuals more accurately than TST, it is possible to diagnose TB infection efficiently in contact investigation so on. However, as same as TST, QFT cannot discriminate between remote infection and recent infection, nor between progressive infection and controllable recent infection. Since QFT is newly development TB diagnosis test, there are many subjects in the QFT test system. For example, one subject is that accurate QFT results among immunocompromised populations are difficult to obtain because of weak immune responses. After these many research data are accumulated, we will be able to have many solutions in QFT.