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)

Testing for a mycobacterial infection relies on detecting a cell-mediated immune response to mycobacterial antigens. The purified protein derivative (PPD) skin test assesses whether a person has been exposed to Mycobacterium tuberculosis by introducing mycobacterial proteins under the skin and waiting 48–72 hours for a localized induration due to memory T cells. A positive reaction indicates prior exposure or infection (latent or active) but does not distinguish between them or confirm active disease; it merely shows that the immune system has been sensitized to mycobacterial components. It also has limitations, such as false positives in people who have received the BCG vaccine or environmental non-tuberculous mycobacteria, and false negatives in individuals with weakened immune systems. The other tests mentioned target different organisms or toxins (Elek detects diphtheria toxin production; CAMP identifies a toxin-enhanced hemolysis with certain streptococci; Nagler tests lecithinase activity of Clostridium perfringens), so PPD is the one used for assessing mycobacterial exposure.

Testing for a mycobacterial infection relies on detecting a cell-mediated immune response to mycobacterial antigens. The purified protein derivative (PPD) skin test assesses whether a person has been exposed to Mycobacterium tuberculosis by introducing mycobacterial proteins under the skin and waiting 48–72 hours for a localized induration due to memory T cells. A positive reaction indicates prior exposure or infection (latent or active) but does not distinguish between them or confirm active disease; it merely shows that the immune system has been sensitized to mycobacterial components. It also has limitations, such as false positives in people who have received the BCG vaccine or environmental non-tuberculous mycobacteria, and false negatives in individuals with weakened immune systems. The other tests mentioned target different organisms or toxins (Elek detects diphtheria toxin production; CAMP identifies a toxin-enhanced hemolysis with certain streptococci; Nagler tests lecithinase activity of Clostridium perfringens), so PPD is the one used for assessing mycobacterial exposure.