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January NaN, 2002

Interferon Assay Compared to Tuberculin Skin Testing for Latent Tuberculosis Detection

Author Affiliations

Stephen J.LurieMD, PhD, Senior EditorIndividualAuthor

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

To the Editor: Dr Mazurek and colleagues1 concluded that a whole-blood interferon γ (IFN-γ) assay was comparable to tuberculin skin testing (TST) in the detection of latent tuberculosis infection (LTBI). However, the results fail to support their conclusions about the sensitivity or specificity of this assay. The operating characteristics of a new test should be derived by comparison to a reference standard, TST in this case. Results of TST of 15 mm or greater or less than 5 mm reliably identify the presence and absence of LTBI, respectively.2 Thus, the authors should demonstrate that the IFN-γ assay is consistently positive when TST results are 15 mm or greater and negative when TST results are less than 5 mm. These data are not presented, but the absence of a positive assay result in 36% of patients with tuberculosis disease (group 4) and the fact that half of the subjects in the asymptomatic "high risk" group (group 2) have discordant TST and IFN-γ results suggest that both sensitivity and specificity of the assay may be limited. Table 1 should be presented with corresponding data for the assay in each cell.

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