Adapted from Information from Centers for Disease Control and Prevention: http://www.cdc.gov/tb/topic/testing/default.htm
Tuberculosis (TB) is a disease caused by the organism Mycobacterium tuberculosis. There are two kinds of tests that are used to determine if a person has been infected with TB bacteria: the tuberculin skin test (TST) and tuberculin blood tests. A positive TST or TB blood test indicates that a person has been infected with TB bacteria. It does not tell whether the person has latent TB infection (LTBI) or has active TB. Physicians must follow up positive test results with chest radiographs, cytology of sputum, culture of sputum or lavage fluids, biopsy, etc.
Tuberculin Skin Test
The TST is performed by injecting 0.1 mL of tuberculin purified protein derivative (PPD) into the inner surface of the forearm by intradermal injection. A person given the tuberculin skin test must return within 48 to 72 hours to have a trained health care worker look for a reaction on the arm. The health care worker will look for a raised, hard area or swelling, and if present, measure its size using a ruler. Redness by itself is not considered part of the reaction.
The skin test result depends on the size of the raised, hard area or swelling. It also depends on certain risk factors of being infected and of progression to TB disease.
Some persons may not react to the TST even though they are infected with M. tuberculosis. The reasons for these false-negative reactions may include, but are not limited to, the following:
Tuberculin Blood Test
TB blood tests (also called interferon-gamma release assays or IGRAs) measure how certain circulating immune cells react to the bacteria that cause TB. An IGRA measures how strong a person’s immune system reacts to TB bacteria by testing the person’s blood in a laboratory.
Two IGRAs are approved by the U.S. Food and Drug Administration (FDA):
A positive IGRA means that the person has been infected with TB bacteria. Physicians must follow up with additional tests to determine if the person has LTBI or active TB. A negative IGRA means that the person’s blood did not react to the test and that LTBI or TB disease is not likely. However, the IGRA may be falsely-negative in patients with immune suppression due to disease, conditions, or drugs.
IGRAs are the preferred method of TB infection testing for the following:
Who Should Get Tested for TB
1Information from Centers for Disease Control and Prevention: http://www.cdc.gov/tb/topic/testing/default.htm.
Therapeutic Antibodies and Tuberculosis Testing
(The following is not from the CDC website)
Physicians have never before had such a powerful battery of approved and developing immune modulating therapies. Therapeutic antibodies represent some of the most important tools for managing autoimmune and inflammatory conditions. A certain number of these powerful therapeutics also have a profound effect on cellular immune function, vitally important to maintaining normal health and preventing disease such as TB, fungal infections, and parasitic infestations.
Drugs such as the TNF-α inhibitors (i.e., infliximab, adalimumab, certolizumab, golimumab, and etanercept) and other immune-modulating drugs have warnings about the need to test for TB prior to initiating therapy.
However, patients with diseases such as Crohn’s disease, psoriasis and psoriatic arthritis, rheumatoid arthritis, ankylosing spondylitis, and other conditions often have prior treatment with immunosuppressive drugs such as prednisone. These treated patients may not react properly to TSTs.
CANDIN® can help assess a patient’s state of immune suppression or anergy, contributing to interpretation of tests such as TST. Because some persons with normal cellular immunity are not hypersensitive to Candida, concurrent use of other cell-mediated hypersensitivity skin test antigens is recommended.
See Full Prescribing Information.
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