Mycobacterium tuberculosis (MTB) is an infectious agent that usually attacks the lungs, but can attack almost any part of the body. It is spread from person to person through the air by droplets when a person with MTB in their lungs or throat coughs, laughs, sneezes, or even talks. However, significant and repeated contact is usually required for infection. The routine universal testing of all children is no longer recommended because the conditions under which most infections are spread, including poverty and overcrowding, are well described. After a known exposure, high-risk or symptomatic patients are encouraged to undergo screening.

The tuberculin skin test is one method to determine if a person has TB. Although there are several skin tests available, the preferred method is known as the Mantoux test, which involves intradermal administration of 0.1 mL of 5 tuberculin units (TU) as a partial protein derivative (PPD), usually at the flexor surface (dorsal or volar) of the forearm. The test should be read 48 to 72 hours after administration, and the transverse diameter of induration should be measured in millimeters.