Final answer:
The Mantoux test for TB is positive if a certain size of induration is seen at the injection site.
Step-by-step explanation:
The Mantoux tuberculin skin test is used to screen for potential tuberculosis (TB) exposure. The test involves injecting tuberculin protein derivative into the skin. A positive result is indicated by redness, swelling, or hardness at the injection site, known as induration. The size of the induration is measured, and a positive test is typically defined as having an induration size of 10 mm or greater in most individuals, or 5 mm or greater in those with a high risk of TB exposure (e.g., immunocompromised individuals).