Two tests can be used to help detect TB infection: a skin test or a TB blood test.
The Mantoux tuberculin skin test (TST) is performed by injecting a small amount of fluid (called tuberculin) into the skin in the lower part of the arm. A person given the TST must return within 48 to 72 hours to have a trained healthcare worker look for a reaction on the arm; this must be done in person.
The TB blood test, known as the Interferon Gamma Release Assay (IGRA), measures how the patient’s immune system reacts to the germs that cause TB when present. There are currently two Federal Drug Administration (FDA) approved blood tests on the market: the QuantiFERON®–TB Gold In-Tube test (QFT-GIT) and the T-SPOT®.TB test (T-Spot).
Although the tuberculin skin test has been the most common screening method in Texas, many health departments now use the IGRA test as the standard tool. When choosing a skin test or blood test, consideration can be made based on age, health status (see policy TB 1004), BCG status, and other factors of the person needing the test.
A positive TST or IGRA only tells you if you have TB germs in your body. Other tests may be needed to tell if you have TB disease, such as a chest x-ray (CXR) and other laboratory testing of sputum.