Pseudomembranous colitis is an uncommon but serious inflammation of the colon that can cause diarrhea, dehydration, and even death. It occurs in some people who have been given antibiotics. These drugs destroy harmless bacteria already in the colon that prevent the growth of disease-causing organisms. Subsequent growth of a particular organism, Clostridium difficile, can cause pseudomembranous colitis. This organism produces A and B toxins that can be measured in stool samples. Doctors usually use stool tests that measure toxin A to diagnose colitis rather than stool cultures because cultures often test positive for this organism in people without colitis. Whether the stool tests that are commonly used to detect clostridium toxins miss important strains (types) of clostridium is not well known.