What is the Tuberculin Skin Test (TST)?
The tuberculin skin test was developed over one-hundred years ago and is a test for TB infection. It is also known as the Mantoux test. The TST uses a small needle to inject Purified Protein Derivative (PPD), also sometimes called ‘tuberculin’, into the arm just under the skin. Tuberculin is a mixed protein preparation, which is produced from killed TB bacteria. If a lump (known as an induration) appears at the site of the injection 48-72 hours after the injection, it is measured, and if it is large enough the test is considered to be positive. To increase the accuracy of the test, the size of the lump that is considered positive, is different for different groups of people, depending on whether they have other illnesses or are on certain medical treatments.
