What would indicate a successful outcome of a tuberculin skin test?

The presence of induration at the site of injection is the primary indicator of a successful outcome for a tuberculin skin test, also known as the Mantoux test. This test is employed to assess whether an individual has been exposed to the bacteria that cause tuberculosis (TB).

When the tuberculin antigen is injected, a localized immune response occurs in individuals who have been sensitized to the TB bacteria. Induration, which is a palpable, raised area at the site, signifies that the immune system has reacted to the antigen. The size of the induration, rather than just the redness or swelling, is what is measured to determine the reactivity of the test.

In contrast, a lack of induration suggests no previous exposure and thus a negative result. Minimal swelling or severe redness without induration are not considered appropriate indicators of a positive result. The measurement of induration provides a standardized way to evaluate responses and helps in making clinical decisions regarding further testing or treatment.