Effect of tuberculin skin testing on aMycobacterium tuberculosis-specific interferon-γ assay

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Abstract
Recently, interferon-γ release assays (IGRA) for specific diagnosis ofMycobacterium tuberculosisinfection have become available. In recent UK tuberculosis (TB) guidelines, it has been advised to screen for latentM. tuberculosisinfection using the tuberculin skin test (TST), followed by IGRA if the TST is positive. Since TST can boost immune responses to tuberculin, the present authors evaluated whether TST administration affects the result of QuantiFERON®-TB Gold in-tube (QFT-GIT), a whole blood-based IGRA.QFT-GIT was performed on the day of TST administration and the day of reading in 15 TST-negative subjects, 46 TST-positive subjects with recent or remote exposure toM. tuberculosisand five cured TB patients.No systematic boosting of QFT-GIT responses from negative to positive was observed. Only in a few TST-positive persons did TST enhance pre-existing QFT-GIT responses.Screening for latentMycobacterium tuberculosisinfection using tuberculin skin testing followed by interferon-γ release assays on the day of reading is a reliable approach, as the specificity of QuantiFERON®-TB Gold in-tube is not affected by prior tuberculin skin test administration.