Diagnosis of latent tuberculosis infection: the potential role of new technologies

Tuberculosis (TB) is a major cause of morbidity and mortality worldwide. TB control programmes need improvement in the diagnosis of latent TB infection. The tuberculin skin test (TST) is far from a 'gold' standard as it often gives false results. Interferon-gamma assays are newly available tests to detect latent TB infection, but they are currently not routinely used. They are based on immune responses to purified protein derivative (PPD) or to region of difference 1 (RD1) specific antigens. Assays based on RD-1 specific antigens perform better than both PPD based assays and TST. They correlate with TB exposure and are less likely to give false results in non-tuberculous mycobacterial disease, Bacille Calmette-Guerin (BCG) vaccination and immunosuppression. More accurate diagnosis of latent TB infection with RD-1 specific antigen based interferon-gamma assays may allow targeting of chemoprophylaxis to reduce the burden of active TB while decreasing wastage of health care resources due to false results associated with TST. However, further research and development is required to verify that new tests can predict the risk of later development of active TB and to make it feasible to perform these tests in a reproducible fashion at low cost, particularly in developing countries.