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.

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.