on the ability of the Mycobacterium tuberculosis antigens for early secretory antigen target 6 (ESAT-6) and culture filtrate protein 10 (CFP-10) to stimulate host production of interferon-gamma. Because these antigens are only present in few non-tuberculous mycobacteria or not in any BCG vaccine strain, these tests are thought to be more specific than the tuberculin skin test. The blood tests QuantiFERON-TB Gold In-Tube and T-SPOT.TB use these antigens to detect people with tuberculosis. Lymphocytes from the patient's blood are incubated with the antigens. These tests are called interferon γ tests and are not equivalent. If the patient has been exposed to tuberculosis before, T lymphocytes produce interferon γ in response. The QuantiFERON-TB Gold In-Tube uses an ELISA format to detect the whole blood production of interferon γ. The distinction between the tests is that QuantiFERON-TB Gold quantifies the total amount of interferon γ when whole blood is exposed to the antigens(ESAT-6, CFP-10 and TB 7.7(p4)), whereas Guidelines for the use of the FDA approved QuantiFERON-TB Gold were released by the CDC in December 2005. In October 2007, the FDA gave approval of QuantiFERON-TB Gold In Tube for use in the United States. The enzyme-linked immunospot assay (ELISPOT) is another blood test available in the UK that may replace the skin test for diagnosis. T-SPOT.TB, a type of ELISpot Assay, counts the number of activated T lymphocytes that secrete interferon γ. For diagnosing latent TB, three systematic reviews of IGRAs concluded the tests noted excellent specificity for the tests to distinguish latent TB from prior vaccination. According to a study from Korea, where there is a high prevalence of LTBI, QuantiFERON-TB Gold and T-SPOT.TB have good sensitivity but reduced specificity for diagnosing active TB, due to their ability to detect latent TB. In a recently published metaanalysis, with data from both developed and developing countries, QuantiFERON-TB Gold In Tube had a pooled sensitivity for active TB of 81% and specificity of 99.2%, whereas T-SPOT.TB had a pooled sensitivity of 87.5% and specificity of 86.3%. In head-to-head comparisons, the sensitivity of IGRAs surpassed TST. However, several subsequent studies have reported higher sensitivity for TST than for IGRAs in patients with active TB; one large study reported a sensitivity of 90% for TST and only of 81% for the QuantiFERON-TB Gold assay. A study at Stanford University confirmed that addition of immune boosters can make the IGRA more reliable in terms of separating