Abstract

A new test that measures interferon-γ (IFN-γ) release in whole blood following stimulation with tuberculin has the potential to detect tuberculosis infection using a single blood draw. The IFN-γ release assay was compared with the standard tuberculin skin test (TST) among 467 intravenous drug users at risk for tuberculosis in urban Baltimore. Among 300 human immunodeficiency virus (HIV)—seronegative patients, the IFN-γ release assay was positive in 177 (59%), whereas the TST was positive in 71 (24%), for a percent agreement of 59% (κ = 26%). Among 167 HIV-seropositive subjects, the IFN-γ release assay identified 32 reactors (19%); the TST identified 16 reactors (9.6%), for a percent agreement of 82% (κ = 28%). The IFN-γ release assay detected more reactors than did the TST, but its agreement with TST was weak. As the TST is an imperfect standard, further evaluation of the IFN-γ release assay among uninfected persons and persons with culture-confirmed tuberculosis will be useful.

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