NCIt definition : A test to determine if a subject has ever had a tuberculosis infection. A small amount
of purified tuberculosis protein is placed under the skin of the forearm and a positive
skin reaction indicates previous exposure to Mycobacterium tuberculosis.;
Alternative definition : NICHD: A test of delayed-type hypersensitivity involving injection into the skin of
a small amount of purified protein derivative (PPD). The formation of a specific,
defined amount of induration in response to the test suggests the presence of tuberculosis
infection.;