Latent tuberculosis infection diagnosis has relied for over 100 years on identification of a T-cell specific response by tuberculin skin test (TST). Recently blood-based in vitro interferon-γ release assays (IGRAs) have been developed to overcome the limitations of the skin test: an ELISA-based method (QuantiFERON-TB Gold In-tube) and an ELISPOT-based method (T.SPOT-TB). This paper describes the laboratory method and clinical interpretation of these two new immunodiagnostics, and also reviews the current literature related to their value in the diagnosis of latent tuberculosis infection and active tuberculosis. IGRAs have proved to be more specific than TST in diagnosis of latent TB infection in BCG-vaccinated individuals and have a better predictive value for progression to active tuberculosis. Blood-based IGRAs have limited value in diagnosis of active TB, but T-SPOT.TB in extrasanguinous fluids shows preliminary good diagnostic performance for smear-negative pulmonary and extrapulmonary TB. Skin testing with recombinant M. tuberculosis specific antigens might be an alternative for latent TB infection diagnosis in low-resource environments. There is a need for additional studies in immunocompromised individuals and in high-incidence countries for a better definition of the role of these new immunodiagnostics.
Bumbăcea D, Lungu R, Pele I, Neagu A, Alexiu I, Chivu Economescu M, et al. New immunodiagnostic tests for latent and active tuberculosis. Rev Romana Med Lab. 2011;19(3):267-78