Final answer:
An induration of 15 or more millimeters is a positive result for the Mantoux tuberculin skin test, which is used to determine if a person has been exposed to the bacterium that causes tuberculosis.
Step-by-step explanation:
An induration of 15 or more millimeters is considered positive in the Mantoux tuberculin skin test for tuberculosis (TB). This test is used to detect whether a person has been exposed to Mycobacterium tuberculosis, the bacterium that causes TB.
The test involves injecting a small amount of tuberculin protein derivative into the skin. After 48-72 hours, the injection site is assessed for redness, swelling, or hardness. An induration, which is a hard, raised red area, signifies a positive reaction indicative of a cellular immune response to the pathogen. A positive test, however, does not necessarily mean active infection with TB, as it may also result from a prior infection that has either been cleared or gone into latency.
As such, further evaluation, including assessment of symptoms and radiographic findings, is often warranted to confirm active tuberculosis infection when a positive tuberculin skin test is observed.