**7. Interferon-Gamma Release Assays (IGRA)**

Because of the difficulties with the tuberculin test interpretation, the interferon-gamma assay test was developed. Two available formats of the interferon-gamma release assays are; the Quantiferon-TB Gold and T Spot-TB test. The IGRA assay is based on the ability of the MTB antigens, which includes the Early Secretory Antigen Target 6 (ESAT-6) and Culture Filtrate Protein 10 (CFP-10) to stimulate host production of interferon –gamma. These antigens are not present in NTM or in BCG vaccine, so, these tests can distinguish latent TB infection from BCG immunization and NTM infections. Requiring a single visit to draw a blood sample and result available within 24 hours are main advantages. It does not boost immune response measured by subsequent tests which can happen with tuberculin skin test. It does not cause to readers bias as in tuberculin skin test and not affected by prior BCG vaccination. Blood must be processed within 12 hours while leu‐ kocytes are still viable. There are limited data for sensitivity of IGRAs in children young‐ er 17 years of age and immunocompromised patients e.g. HIV/AIDS, diabetics, treatment with immunosuppressive drugs [29].
