label: Positive tuberculin skin test
label_lc: positive tuberculin skin test
description: "A positive result of the tuberculin skin test suggesting previous expouse or infection with mycobacterium teberculosis. A standard dose of five tuberculin units (TU) (0.1ml) is injected intradermally (into the skin) and read 48 to 72 h later. A person who has been exposed to the bacteria is expected to mount an immune response in the skin containing the bacterial proteins. The volar aspect of the forearm is the preferred site of test. The basis of reading is the presence or absence of induration, which may be determined by inspection (from a side view against the light as well as by direct light) and by palpation. For standardization, the diameter of induration should be measured transversely to the long axis of the forearm and recorded in millimeters."