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November 21, 2012

Interferon-γ-Release Assays for Latent Tuberculosis

JAMA. 2012;308(19):1971. doi:10.1001/jama.2012.12817

To the Editor: The Viewpoint by Drs LoBue and Castro1 regarding latent tuberculosis infection and the use of interferon-γ-release assays (IGRAs) does not discuss another potential advantage of these blood tests: to reduce the possibility of false-negative or uninterpretable nonreactive purified protein derivative (PPD) tests due to anergy.

As the population ages, many persons develop acute and chronic illnesses and may be exposed to immunomodulating therapies. In such situations, a negative PPD test may not ensure the absence of tuberculosis but merely reflect an acquired biological inability to respond to the protein antigen. The addition of anergy panel agents to the skin testing regimen increases the expense and complexity. Also, these agents are not routinely available in most primary care outpatient settings.