QuantiFERON TB Gold (QFT-G) is a United States Food and Drug administration (FDA) approved enzyme-linked immunosorbent assay (ELISA). It is a modified QFT-G with an in-tube collection system consisting of three tubes, nil, TB antigen, and mitogen. This is an in-vitro diagnostic test using synthetic peptides simulating early secretory antigen target-6 (ESAT-6), culture fibrate protein-10 (CFP-10), and TB 7.4 (p4) which are two M. tuberculosis proteins.
Fresh heparinized blood collected within 12 hours of the test is incubated with the above antigens for 16 to 24 hours, after which the amount of IFN-gamma is measured. The white blood cells of a patient infected with M. tuberculosis will release interferon -gamma (IFN-gamma) in response to contact with the TB antigens.
Because these proteins are absent from all Bacillus of Calmette-Guerin (BCG) vaccine strains and from commonly encountered nontuberculous mycobacteria (NTM) except for Mycobacterium kansasii, szulgai, and marinum, QFT-G is expected to be more specific for Mycobacterium tuberculosis than tests that use tuberculin purified protein derivatives (PPD) as the antigen. QFT–G is indicated for diagnosing latent TB infection (LTBI) and active TB disease with Mycobacterium tuberculosis.
(Guidelines for Using QuantiFERON-TB Gold Test for Detecting Mycobacterium Tuberculosis Infection,United States. Mortality and Morbidity Weekly Reports, Volume 54. pp 49 -55, December 2005).