Final answer:
A positive result of a tuberculin test is indicated by induration, a raised red area on the skin that is hard to the touch. It is caused by an accumulation of activated macrophages and signifies exposure to M. tuberculosis.
Step-by-step explanation:
A positive result of a tuberculin test is indicated by induration. Induration refers to a raised red area on the skin that is hard to the touch. This reaction occurs a couple of days after the injection of bacterial proteins from M. tuberculosis. Induration is caused by an accumulation of activated macrophages, and it indicates that the patient has been exposed to the bacteria and has a cellular immune response to it.