Letters Section Editor: Jody W. Zylke, MD, Senior Editor.
Author Affiliations: Division of Tuberculosis Elimination, Centers for Disease Control and Prevention, Atlanta, Georgia (email@example.com).
In Reply: Dr Rosch suggests that another advantage of IGRAs over the tuberculin skin test (TST) is that IGRAs may also test for nonspecific immune response, which is not routinely done with TST. However, at the present time there is no evidence to suggest that this is the case.
In addition to measuring response to simulated Mycobacterium tuberculosis antigens, IGRAs also incorporate a negative control (response to solution with no antigens) and positive control (response to a nonspecific mitogen). It is expected that a large majority of persons with intact immunity will respond by producing interferon γ when exposed to the mitogen, so the mitogen response serves as a crude measure for assessing overall cell-mediated immunity.
LoBue PA, Castro KG. Interferon-γ-Release Assays for Latent Tuberculosis—Reply. JAMA. 2012;308(19):1971. doi:10.1001/jama.2012.12826