Do IFN-γ-release assays predict the risk of TB? New evidence from a study on patients with silicosis

IFN-γ-release assays (IGRAs) are new tools for the diagnosis of latent TB infection which, until recently, relied only on the use of the tuberculin skin test (TST). However, while the positive predictive value of a positive TST for active TB is well established, little evidence on this issue is available for IGRAs. In a study conducted on silicosis patients in Hong Kong, China, Leung et al. found that a positive response to an IGRA, the T-SPOT.TB, was associated with a larger than fourfold increase in the risk of developing TB compared with those who tested negative, while a smaller than twofold increase was observed for TST-positives compared with negatives. This study provides further support to the guidelines from public health agencies recommending the use of IGRAs in place of or in addition to TST. Several issues regarding their optimal use, however, remain open to debate.