A test to determine the presence of infection with tuberculosis (TB). A solution containing purified protein derivative of TB is injected intradermally into the arm, and the response is read 48 to 72 hr later. A 5-mm induration is considered a positive reaction if the patient has been in close contact with persons infected with TB, is infected with human immunodeficiency virus (HIV), has risk factors for HIV, or has a chest x-ray examination that suggests a history of pulmonary TB. A 10-mm induration is considered positive in people born in nations where TB is endemic, in nursing home patients, in patients with other serious illnesses, and in people of low socioeconomic status. In all other people, a 15-mm induration is considered a positive result. A positive response indicates infection but does not distinguish between active infection and that which has been controlled by the immune system or drugs.