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Letters
January 23/30, 2002

Interferon Assay Compared to Tuberculin Skin Testing for Latent Tuberculosis Detection—Reply

Author Affiliations
 

Stephen J.LurieMD, PhD, Senior EditorIndividualAuthor

JAMA. 2002;287(4):450-452. doi:10.1001/jama.287.4.447

In Reply: The whole blood IFN-γ assay was compared to the TST as suggested by Drs Hersh and von Reyn. Limiting our comparison to the subgroups they suggest does increase agreement as shown in Table 1. Regardless, limiting the comparison to TST results of 15 mm or greater or less than 5 mm does not reliably identify the presence and absence of LTBI or TB. For example, Al Zahrani et al1 reported that for TST, the magnitude of induration greater than 5 mm was not related to diagnosis and that 43% of people with active TB had reactions less than 15 mm. Judson and Feldman2 provide evidence that large TST reactions may arise from reactivity to nontuberculous mycobacteria (NTM). Additionally, TST responses of less than 5 mm may occur in as many as 20% of patients with culture-confirmed TB.3

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