TB testing has traditionally relied on a skin test that was developed over 100 years ago.5 However, a simple blood test can now get the job done as well.
A TB skin test, also called the Mantoux tuberculin skin test (TST), can be completed at our center. During the test, a small amount of fluid called tuberculin is injected into the skin on the lower part of the arm.6 The person must then return within 48 to 72 hours to have a healthcare provider look for a reaction on the arm. Depending on the size of the raised, hard area, swelling, and risk factors, the healthcare provider will determine if the test was positive or negative.6 A positive result may mean the person is infected with TB bacteria. However, there are factors that can cause false positives, such as prior BCG vaccination, a TB vaccine that many people born outside the U.S. receive. In the case of a positive result, more testing, such as a chest X-ray, sputum culture, or both, may be performed to determine the presence of active TB disease.13
TB blood tests are also called interferon-gamma release assays, or IGRAs. IGRAs are whole-blood tests that can aid in diagnosing TB infection.3 Unlike the TB skin test, TB blood tests are completed in a single visit to a healthcare professional, making them easier and more convenient for employers and employees. TB blood tests can also be a more accurate form of TB testing.
During a TB blood test, a healthcare provider draws a patient’s blood and sends it to a laboratory for analysis and results. A positive result means the person is infected with TB bacteria, but additional tests are needed to determine if the person has LTBI or TB disease.
