Comparison of two commercial interferon-γ assays for diagnosingMycobacterium tuberculosisinfection

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Abstract
The clinical usefulness ofex vivointerferon-γ assays may largely depend on the assay format and epidemiological status of tuberculosis (TB) in the region studied.From July 2004 to June 2005 a prospective comparison study was undertaken at a tertiary referral hospital in South Korea. The results of tuberculin skin tests (TST) and the commercially available QuantiFERON-TB Gold (QFT-G) and T SPOT-TB (SPOT) assays were compared in an intermediate TB-burden country.Of the 224 participants studied, results from all three tests (TST, QFT-G, and SPOT) were available in 218; 87 with active TB and 131 at a low risk for TB. Using 10 mm as a cut-off for TST, SPOT sensitivity (96.6%) was significantly higher than that seen for TST (66.7%) and QFT-G (70.1%). QFT-G showed superior specificity over TST (91.6versus78.6%). Although the specificity of QFT-G was higher than that of SPOT (91.6versus84.7%), the difference was not statistically significant.Whilst some differences were found in the performance of the two commercialised interferon-γ assays, they seemed to be superior in their detection ofMycobacterium tuberculosisinfection compared with tuberculin skin tests. The most appropriate choice of interferon-γ assay to use may depend on the clinical setting.

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