Currently, there are three commercial diagnostic tests for LTBI: the Tuberculin Skin Test (TST), which for decades was the only method for detecting TB infection, and two techniques introduced relatively recently that are based on the detection of interferon-gamma (IFN-G) released from sensitized lymphocytes against specific antigens of M. tuberculosis: Quantiferon®-TB Gold in-Tube (QFT) and T-SPOT®.TB (T-SPOT). Here, IFNG is linked to tuberculosis.