[Update on tuberculosis: interferon-gamma assays]

Until recently, skin testing with purified protein derivative of tuberculin was the only practical way of detecting latent tuberculosis infection (LTBI). However, the tuberculin skin test (TST) is subject to considerable variations and other limitations. PPD is a mixture of more than 200 mycobacterial antigens also present in nontuberculous mycobacteria and in the Bacille Calmette-Guérin (BCG) vaccine strains. Therefore false-positive testing results were common. Recently, peripheral blood-derived T-cell interferon-gamma responses to M.tuberculosis-specific antigens have been investigated for the management of tuberculosis. The results suggest that interferon-gamma assays may have advantages over the TST, in terms of higher specificity, better correlation with exposure to M.tuberculosis, and less cross-reactivity due to BCG vaccination and non-tuberculous mycobacterial infection. Furthermore, the interferon-gamma assays are less subject to reader bias and error and can be accomplished after a single patient visit. However, there is inadequate evidence on the value of interferon-gamma assays in the management of immunocompromised individuals for whom an alternative assay to the TST would be of great value.