PPD skin test (Purified Protein Derivative)

The PPD skin test, also called the tuberculin skin test, checks if someone has been exposed to tuberculosis (TB). A small amount of a protein mixture from TB bacteria is injected under the skin, usually on the forearm. If the person has been exposed or vaccinated against TB, their immune system reacts by creating a small lump or swelling at the injection site within 48-72 hours. The size of the swelling helps doctors determine whether a person has latent TB infection or needs further testing. The test is safe and widely used for TB screening.