DefinitionThe PPD skin test is a method used to diagnose tuberculosis (TB). PPD stands for purified protein derivative.Alternative NamesPurified protein derivative standard; TB skin test; Tuberculin skin test; Mantoux testHow the test is performedThe test site (usually the forearm) is cleansed with rubbing alcohol. The PPD extract is then injected under the top layer of skin, causing a welt to form on the skin. This welt usually goes away in a few hours.The reaction will take 48 - 72 hours to develop. You must return to your health care provider within that time to have the area checked. This test will determine whether you have had a significant reaction to the PPD test. The reaction is measured in millimeters of firm swelling (induration), not redness, at the site.How to prepare for the