Tuberculin Skin Test
A tuberculin skin test (also called a Mantoux tuberculin test) is done to see if you have ever been exposed to tuberculosis (TB). The test is done by putting a small amount of TB protein (antigens) under the top layer of skin on your inner forearm. This test is often used when symptoms, screening, or testing, such as a chest X-ray, show that a person may have TB. If you have ever been exposed to the TB bacteria (Mycobacterium tuberculosis), your skin will react to the antigens by developing a firm red bump at the site within 2 days.
A tuberculin skin test cannot tell how long you have been infected with TB. It also cannot tell if the infection is latent (inactive) or if you have active TB that can be passed to others.
Why It Is Done
A tuberculin skin test is done to find out if someone has tuberculosis (TB), including those who:
- Live with or spend time with someone who has TB.
- Were born in or lived in countries where TB is common.
- Live or have lived in crowded conditions where TB can easily spread, such as nursing homes, homeless shelters, or correctional facilities.
- Work in a place where TB can easily spread, such as a hospital or nursing home.
- Have TB symptoms, such as an ongoing cough, night sweats, and unexplained weight loss.
- Have had an abnormal chest X-ray.
- Have had a recent organ transplant or have an impaired immune system from a health condition or from certain medicines.
A tuberculin skin test should not be done for anyone:
- With a known TB infection.
- Who has had a previous severe reaction to the TB antigens used in the test.
- Who has a skin rash that would make it hard to read the skin test.
How To Prepare
In general, there's nothing you have to do before this test, unless your doctor tells you to.
How It Is Done
During the skin test, a small amount of TB protein (antigens) is put under the top layer of skin on your inner forearm. The test will feel like a skin prick. The fluid makes a little bump (wheal) under the skin. A circle may be drawn around the test area with a pen.
Risks
There is a very slight risk of having a severe reaction to the tuberculin skin test, especially if you've had tuberculosis (TB). An allergic reaction can cause a lot of swelling and pain at the site. You may have a sore.
You cannot get a TB infection from the tuberculin skin test. That's because no live bacteria are used for the test.
A tuberculin skin test is safe during pregnancy or breastfeeding.
Results
Redness alone at the skin test site usually means you haven't been infected with TB bacteria. The size of the firm bump (not the red area) is measured 2 to 3 days after the test to find out the result.
Your risk of having TB is used along with the size of the bump to determine whether the test is:
- Positive, meaning you have been infected with TB bacteria. A firm bump that is 5 mm or larger in size has formed at the test site. A positive reaction can usually be seen for about 1 week.
- Negative, meaning you have not been infected with TB bacteria. No firm bump forms at the test site, or a bump forms that is smaller than 5 mm.
A positive tuberculin skin test doesn't mean you have contagious (active) TB. The test can't tell whether you have active or inactive (latent) TB. It also can't tell the difference between a TB infection and a TB vaccination (BCG vaccination). More tests—such as a chest X-ray, a sputum culture, or both—are usually done to see if you have an active TB infection.
Credits
Current as of: September 25, 2025
Author: Ignite Healthwise, LLC Staff
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