Tuberculin Skin Tests vs. Interferon-γ Release Assays, Redux

For nearly a century, the tuberculin skin test (TST) has been used for diagnosing active TB and latent Mycobacterium tuberculosis infection (MTBI). However, the TST has substantial problems, including delay in obtaining results and false-positive results due to infection with nontuberculous mycobacteria. The FDA has approved two in vitro interferon-γ release assays (IGRAs) that measure interferon-γ release by lymphocytes after incubation with mycobacterial antigens. The QuantiFERON-TB (QFT) assay, like the TST, uses PPD as the antigen. The QuantiFERON-TB Gold (QFT-G) assay uses synthetic peptides representing two M. tuberculosis proteins that are absent from bacille Calmette-Guérin vaccines and from most nontuberculous mycobacteria. Presuma…