Tuberculin Skin Test

A tuberculin skin test is done to see if you have ever had Reference tuberculosis (TB) Opens New Window. The test is done by putting a small amount of TB protein (Reference antigens Opens New Window) under the top layer of skin on your inner forearm. 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.

The TB antigens used in a tuberculin skin test are called purified protein derivative (PPD). A measured amount of PPD in a shot is put under the top layer of skin on your forearm. This is a good test for finding a TB infection. It is often used when symptoms, screening, or testing, such as a chest Reference X-ray Opens New Window, show that a person may have TB.

A tuberculin skin test cannot tell how long you have been infected with TB. It also cannot tell if the infection is Reference latent Opens New Window (inactive) or is active and can be passed to others.

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