Is the new TB antigen-based skin test ready for use as an alternative to TST/IGRA for TB diagnosis? A narrative review.

In recent years, novel specific Mycobacteria Tuberculous antigen-based skin test (TBST) has become available for clinical use. The mechanism of TBST is similar to the interferon gamma release assay (IGRA), making them potential alternative for identifying latent tuberculous infection (LTBI), especially in subjects with history of BCG vaccination. Three different commercial brands have been developed in Denmark, Russia and China. Clinical studies in the respective countries have shown promising sensitivity, specificity and safety profile. Some studies attempted to address the applicability of TBST in specific subject groups but the discrepancy in defining LTBI and problematic methodologies undermine the generalisation of the results to other communities across the world. Limited cost effectiveness studies for TBST have been conducted without exploring the health economics for preventing development of LTBI into active TB. Unlike IGRA, no clinical studies have addressed the correlation of TBST results (magnitude of induration) with the likelihood of development of active TB. Moreover, the different TBSTs are not widely available for clinical use. While TBST is a promising test to overcome the shortcomings of tuberculin skin tests, more clinical data are needed to support its general application globally for the diagnosis of LTBI.