Which test would be appropriate in the diagnosis of a mycobacterial infection?

Which test would be appropriate in the diagnosis of a mycobacterial infection?

• A. Elek test
• B. CAMP test
• C. Nagler test
• D. PPD test

Answer: (D)

The test being used to diagnose mycobacterial infection is the PPD skin test. It uses intradermal injection of purified protein derivative from Mycobacterium tuberculosis. If a person has been exposed and has a T-cell–mediated (delayed) hypersensitivity to mycobacterial antigens, a localized induration develops within 48–72 hours. A positive result suggests prior infection or exposure, which can reflect latent tuberculosis or a recent exposure; it does not by itself confirm active disease, so further testing with sputum analysis, culture, molecular methods, or imaging is often needed. The other tests listed are not for mycobacteria: the Elek test detects diphtheria toxin production, the CAMP test identifies a synergistic reaction with Group B Streptococcus, and the Nagler test detects lecithinase activity of Clostridium perfringens.