Tuberculosis skin test facts
- The tuberculosis skin test is also known as the tuberculin test or PPD test.
- The PPD test is used to determine if someone has developed an immune response to the bacterium that causes tuberculosis (TB).
- The standard recommended tuberculin test is the Mantoux test, which is administered by injecting a 0.1 mL of liquid containing 5 TU (tuberculin units) PPD (purified protein derivative)into the top layers of skin of the forearm.
- Skin tests should be read 48-72 hours after the injection.
- The basis of the reading of the skin test is the presence or absence and the amount of induration (localized swelling).
- A negative test does not always mean that a person is free of tuberculosis.
- A person who received a BCG vaccine (administered in some countries but not the U.S.) against tuberculosis may also have a positive skin reaction to the TB test.