PPD skin test

The purified protein derivative (PPD) is an antigen used to aid in the diagnosis of tuberculosis infection. An infection with the bacteria that causes tuberculosis frequently leads to a sensitivity to these antigens.

Purified protein derivative standard; TB skin test; Tuberculin skin test

The test site (usually the forearm) is cleansed. The PPD extract is then injected into the most superficial layer under the skin resulting in a blister on the skin.

Because the reaction will take 48 - 72 hours to develop, you must return to your health care provider within that time for a proper evaluation of the test site. This will determine whether you have had a significant reaction to the PPD test. A reaction is measured in millimeters of induration (hard swelling) at the site.

There is no special preparation for this test. Inform your health care provider if you have ever had a positive PPD skin test. If so, you should not have a repeat PPD test. Notify your health care provider if you are taking certain drugs such as steroids or have a medical condition that can affect your immune system such as cancer. Your PPD may be falsely negative or the standards for interpreting a reaction may be different.

There will be a brief sting as a needle is inserted just below the skin surface.

The test is performed to evaluate infection with tuberculosis.