A tuberculin skin test is done to see if
you have ever had
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. 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
X-ray, show that a person may have TB.
tuberculin skin test cannot tell how long you have been infected with TB. It
also cannot tell if the infection is
latent (inactive) or is active and can be passed to