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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. [citation needed] The blood tests QuantiFERON-TB Gold In-Tube and T-SPOT.TB use these antigens to detect people with tuberculosis.
The Quantiferon-TB Gold test (QFT-G) is a whole-blood test for use as an aid in diagnosing Mycobacterium tuberculosis infection, including latent tuberculosis infection (LTBI) and tuberculosis (TB) disease. [15] This test was approved by the U.S. Food and Drug Administration (FDA) in 2005.
The results of this test must be interpreted carefully. The person's medical risk factors determine at which increment (5 mm, 10 mm, or 15 mm) of induration the result is considered positive. [12] A positive result indicates TB exposure. 5 mm or more is positive in An HIV-positive person; Persons with recent contacts with a TB patient
T-SPOT.TB counts the number of antimycobacterial effector T cells, white blood cells that produce interferon-gamma, in a sample of blood.This gives an overall measurement of the host immune response against mycobacteria, which can reveal the presence of infection with Mycobacterium tuberculosis, the causative agent of tuberculosis (TB).
Diagnosis of latent TB relies on the tuberculin skin test (TST) or blood tests. [10] Prevention of TB involves screening those at high risk, early detection and treatment of cases, and vaccination with the bacillus Calmette-Guérin (BCG) vaccine. [3] [4] [5] Those at high risk include household, workplace, and social contacts of people with ...
For example, in patients with cutaneous adverse drug reactions, the challenge of peripheral blood lymphocytes with the drug causing the reaction produced a positive test result for half of the drugs tested. [2] There are currently two IFN-γ release assays available for the diagnosis of tuberculosis:
Grade 4 – disc >10 mm with or without blistering (strongly positive) Grades 1 and 2 could result from previous BCG or avian tuberculosis, rather than human TB infection. Children who were found to have a grade 3 or 4 reaction were referred for X-ray and follow-up. For interpretation of the test, see Tuberculosis diagnosis.
The test is then read 48 to 72 hours later by measuring the size of the largest papule or induration. Indications are usually classified as positive, negative, or doubtful. [2] Because it is not possible to control precisely the amount of tuberculin used in the tine test, a positive test should be verified using the Mantoux test. [3]
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