The PPD skin test is a method used to diagnose tuberculosis. PPD stands for purified protein derivative.

The test site (usually the forearm) is first cleansed. The PPD extract is then injected under the top layer of skin, causing a blister to form on the skin. The reaction takes 48 to 72 hours to develop. Those who receive the injection must return to their health care providers within that time to have the test site checked to determine whether the reaction is significant. A reaction is measured in millimeters of hard swelling (induration) at the injection site.

No special preparation is needed for this test.

Tell your health care provider if you have ever had a positive PPD skin test. If so, you should not have a repeat PPD test.

Tell your health care provider if you have a medical condition or if you take certain drugs, such as steroids, that can affect your immune system. These situations may lead to inaccurate test results.