A nurse is assessing a client who received a Mantoux skin test 72 hr ago for tuberculosis screening. Which of the following findings indicates a positive test result?

Rationale: A. A blister-like area: Blistering is not the expected reaction used to interpret a Mantoux test. The result is based on the presence and size of induration, not the formation of blisters. B. A cool, blanched area: Coolness and blanching are not indicators of a positive test. These findings may reflect poor circulation or local skin reaction unrelated to tuberculosis screening. C. An elevated, hardened area: Induration (elevated, firm area) at the injection site, measured in millimeters, is the basis for determining a positive result. The size threshold for positivity depends on the client’s risk factors for tuberculosis. D. An area of ecchymosis: Bruising at the site is a local skin reaction that can occur after any injection and is unrelated to the diagnostic criteria for a positive Mantoux test.