Tuberculin Skin Test (TST)
The TST utilizes 0.1 mL of purified protein derivative (PPD), which is injected intradermally on the arm. The needle tip is inserted so that the needle is visible under the first layer of skin, bevel up. The PPD is injected slowly to produce a small wheal measuring 5-6 mm in diameter.
The TST is read 48-72 hours after injection by a trained health care worker, such as a physician or nurse. The diameter of any induration is measured in millimeters.
Records of the test are kept in the individual's health record for future reference.