The diagnosis of pseudomembranous colitis, Clostridioides difficile-associated disease, is often made by which method?

• A. Serology
• B. Culturing blood specimens
• C. Nucleic acid amplification test of stool sample
• D. Acid-fast stain of fecal material

Answer: (C)

Pseudomembranous colitis from Clostridioides difficile is diagnosed by detecting the organism’s toxin genes directly in the stool. The nucleic acid amplification test (NAAT) searches for the genes that encode C. difficile toxins, offering rapid and highly sensitive identification of toxin-producing strains. This aligns with the disease mechanism, since the toxins cause the colitis, and stool is the appropriate specimen because the organism and its toxins are localized in the intestinal tract.

Serology looks for antibodies to the toxins and is not helpful for acute diagnosis because antibody responses don’t reliably reflect current infection. Culturing blood specimens won’t detect C. difficile, which typically remains in the gut rather than circulating in крови. An acid-fast stain is not relevant to C. difficile.