Which term refers to a test that uses a skin reaction to detect tuberculosis infection?

• A. Apex
• B. Pleuritis
• C. Tuberculin test
• D. Dyspnea

Answer: (C)

The tuberculin skin test detects TB infection by eliciting a skin reaction to tuberculin. A small amount of purified protein derivative is injected under the skin, and after about 48 to 72 hours the size of the induration (not the redness) is measured. A positive induration means the person has been exposed to TB and has mounted an immune response, which could indicate latent infection or previous vaccination; it does not by itself prove active disease. This test is specifically about immune reaction in the skin to TB antigens, unlike terms that refer to lung anatomy, pleural inflammation, or breathing symptoms.