From the Arm to the Test Tube: Laboratory's New Role in Tuberculosis Testing

For over 100 years, the only diagnostic test for tuberculosis was the tuberculin skin test (TST), which has poor specificity. Individuals who were Mycobacterium bovis BCG-vaccinated often produced a response similar to that induced by infection with Mycobacterium tuberculosis. Approximately 10 years ago, a new method was introduced to determine the in vitro cellular immune responses to M. tuberculosis to aid in the diagnosis of latent tuberculosis. Currently, there are two blood-based gamma interferon-release assays (IGRAs), QFT-Gold assays and T-SPOT.TB. In studies on adults, these assays appear to have greater sensitivity and specificity than the TST. This change in testing has shifted the labor of testing for tuberculosis from the clinical site to the laboratory. This article evaluates the performance of IGRAs as screening tools for latent disease in all patient populations, including children and immunosuppressed adults.