Comparison between a whole blood interferon-gamma release assay and tuberculin skin testing for the detection of tuberculosis infection among patients at risk for tuberculosis exposure

A new test that measures interferon-gamma (IFN-gamma) release in whole bloo d following stimulation with tuberculin has the potential to detect tubercu losis infection using a single blood draw. The IFN-gamma 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 im munodeficiency virus (HIV)-seronegative patients, the IFN-gamma release ass ay was positive in 177 (59%), whereas the TST was positive in 71 (24%), for a percent agreement of 59% (kappa = 26%), Among 167 HIV-seropositive subje cts, the IFN-gamma release assay identified 32 reactors (19%); the TST iden tified 16 reactors (9.6%), for a percent agreement of 82% (kappa = 28%), Th e IFN-gamma release assay detected more reactors than did the TST, but its agreement with TST was weak, As the TST is an imperfect standard, further e valuation of the IFN-gamma release assay among uninfected persons and perso ns with culture-confirmed tuberculosis will be useful.