The diagnosis of pseudomembranous colitis is most rapidly and accurately made by detecting what in stool?

• A. Serology
• B. Assays to detect toxin in stool
• C. Culturing blood specimens
• D. Acid-fast stain of fecal material

Answer: (B)

Pseudomembranous colitis is caused by toxin-producing Clostridioides difficile, so the most reliable and quickest way to confirm the diagnosis is to detect the toxin directly in the stool. The presence of toxin correlates with active disease and provides direct evidence that the bacteria’s poisons are in the gut lumen, driving the inflammation and pseudomembrane formation. Tests that look for the host’s immune response (serology) don’t reflect current infection and aren’t useful for rapid diagnosis. Culturing blood specimens isn’t relevant because C. difficile is an intestinal pathogen and does not typically appear in blood. An acid-fast stain wouldn’t identify the organism or its toxin either. Therefore, stool toxin detection offers the fastest and most accurate diagnostic information for this condition.