What Is the Tuberculin Skin Test?

TB is short for Mycobacterium tuberculosis, or tuberculosis. It’s a bacteria that tends to attack the lungs, but it can affect any part of the body, like the kidneys, the spine, or the brain.

Many people who have TB don’t have any symptoms. They have what doctors call “latent TB.” The tuberculin skin test (also called the Mantoux tuberculin test) can tell if you have this form of the infection.

Here’s how it works: Your doctor uses a small needle to inject some harmless fluid called tuberculin under the skin on your arm. In 2 or 3 days, he’ll check your arm.

What Do the Results Mean?

After the waiting period has passed, you may have a hard, raised bump at the site of the injection. That means you likely have TB germs in your body. Your doctor may do more tests to be sure. These could include blood tests or an X-ray of your chest. He may also want to test your sputum -- that’s the gunk you cough up. Urine or tissue samples can also tell your doctor if the TB germs have begun to spread, or become “active.”

If there’s no bump at the injection site (or a very small one), that likely means you don’t have TB. But if you were infected recently, your body’s natural defenses (your immune system) may not react to the skin test just yet. In that case, your doctor may want you to have another TB skin test in 8 to 10 weeks.

If you test positive, you'll need to take medication -- for several months, in most cases -- to cure it.

WebMD Medical Reference Reviewed by Jennifer Robinson, MD on December 22, 2018

Sources

SOURCES:

CDC: “Tuberculosis (TB),” “Questions and Answers About Tuberculosis.”

Minnesota Department of Health: “The TB (Tuberculosis) Skin Test (Mantoux).”

Mayo Clinic: “Tuberculosis Diagnosis.”

© 2018 WebMD, LLC. All rights reserved.