By Gary M. White, MD
Quantiferon-Tb gold (QFG) is a cocktail of 3 mycobacterial proteins which stimulate the patient's T-cells in vitro to release interferon-gamma, which is then measured using ELISA technology. The test detects infections produced by the M. tuberculosis complex (including M. tuberculosis, M. bovis, and M. africanum infections). BCG strains and the majority of other non-tuberculosis mycobacteria do not harbor ESAT-6, CFP-10, and TB 7.7 proteins; thus, patients either vaccinated with BCG or infected with most environmental mycobacteria should test negative. Results should always be interpreted in conjunction with other clinical and laboratory findings. Some studies show Interferon gold release assays (IGRA) more sensitive than TB skin tests (TST) in detecting Tb infection in adults. It is certainly more specific. In one study of children with documented Tb infection, IGRA and TST are equally sensitive, but IGRAs are more specific [BMC Infectious disease 2016;16;131].