What is a TB Skin Test (TST)?
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A TB skin test is also known as a tuberculin skin test (TST). It shows if you have been exposed to the TB germ and have it in your body. This test is also called a Mantoux test. It is not a vaccine. A TST is safe for pregnant women. You can still have a test if you had a BCG vaccine in the past.
Before you have a TST, tell your health care provider if you:
- Have been treated for TB disease or latent TB infection (LTBI) in the past.
- Have had a positive TB skin test in the past. If you have, you should give proof of the test results.
- Are taking medication that weakens your immune system (e.g., corticosteroids or immunosuppressive agents).
- Have received any live vaccines within the past 4-6 weeks [e.g., yellow fever, measles, mumps, rubella (MMR), or varicella (chickenpox)].
The TST requires two visits to a health care provider:
First visit: The health care provider will inject a small amount of fluid called tuberculin, just under the skin of your forearm. A small raised area will form at the injection site. Do not cover it with cotton or a bandage. The raised area should flatten again in 15 to 30 minutes. You can still do all your normal activities after the test (e.g., shower or bathe). The arm will rarely be itchy or sore after the test. If it is, do not scratch it. You can use a cold cloth, if needed.
Second visit: The health care provider will look at and touch the test spot in 48 to 72 hours (2 to 3 days). Redness can be normal and it does not mean that you were exposed to TB. If a bump is felt, it will be measured. It is a positive reaction if the bump is over a certain size. If the test result is negative, some schools or workplaces will require a second TST to be done (two-step TST).