Effect of tuberculin skin testing on a Mycobacterium tuberculosis-specific interferon-gamma assay.

Recently, interferon-gamma release assays (IGRA) for specific diagnosis of Mycobacterium tuberculosis infection have become available. In recent UK tuberculosis (TB) guidelines, it has been advised to screen for latent M. tuberculosis infection 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 to M. tuberculosis and 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 latent Mycobacterium tuberculosis infection using tuberculin skin testing followed by interferon-gamma 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.