Antigen-based skin testing for TB infection diagnosis

Novel specific Mycobacteria Tuberculous antigen-based skin test (TBST) has been available in Denmark, Russia and China in recent years. Intuitively, TBST is the in-vivo version of IGRA as the principle of TBST is similar to the interferon gamma release assay (IGRA). Thus, TBST is an alternative for identifying tuberculous infection (TBI), especially in subjects with history of BCG vaccination. Majority of the clinical studies have shown promising sensitivity, specificity and safety profile. However, there are still some clinical questions that need to be addressed before the TBST can replace the conventional tuberculin skin test (TST). For example, no clinical studies have addressed the predictive value of TBST with the development of active TB, and there are hardly any studies powered to show the cost effectiveness of TBST on the health economics for preventing development of TBI into active TB. Moreover, generalisation of the test results to general population is problematic as the methodologies and subjects in clinical studies are very heterogeneous. For example, some studies are retrospective with biased samples with high probability of TBI. TST and IGRA were used as the gold standard for comparison, the clinical implication of some of the discordant results were not clear. Therefore, although TBST is a promising test which overcomes some shortcomings of TST, more clinical data are needed to support its general application globally.