INTERFERON GAMMA RELEASE ASSAYS (IGRAs)

• IGRAs are used to screen for TB infection and not to diagnose TB disease.


• Recently, two in-vitro assays that measure interferon release in response to TB specific antigens have become commercially available. These are QuantiFERON-TB Gold In-Tube® and T-SPOT.TB®.


• IGRAs are more specific than the TST due to lack of cross-reactivity from BCG vaccination and sensitization by non-tuberculous mycobacteria.


• IGRAs have shown better correlation than the TST with exposure to M. tuberculosis when used in contact investigations in low incidence settings (Ref.)


• In high burden settings these tests are not as useful and WHO has recommended against their use in such settings.