What Is TB Testing?
TB testing is used to determine if an individual has been infected with the bacteria that cause tuberculosis (TB). The most common methods for TB testing are the Mantoux tuberculin skin test (TST) and the Interferon-Gamma Release Assays (IGRAs), such as the QuantiFERON-TB Gold test. The TST involves injecting a small amount of tuberculin purified protein derivative (PPD) into the skin of the forearm and checking the injection site for a reaction after 48 to 72 hours. A raised, hard area at the injection site may indicate TB infection.
IGRAs are blood tests that measure the immune system’s response to TB bacteria. These tests are preferred in some cases because they require only one visit and are not affected by prior Bacillus Calmette-Guérin (BCG) vaccination, which can cause false-positive results in the TST. Positive results from either test indicate TB infection and usually lead to further testing, such as chest X-rays and sputum tests, to determine if the infection is active or latent and to guide appropriate treatment.
