Clostridium difficile is a normal bacteria found in the intestine. However, after treatment with broad-spectrum antibiotics, the bacteria can become very abundant in the intestine and cause diarrhea that is often severe and accompanied by fever, pain and other complications. C. difficile secretes two toxins, A and B, which cause the symptoms and complications of the infection. Because culturing the bacteria is complicated, a rapid test for the bacteria’s antigen and toxins A and B is used. For both tests, results are reported as positive, negative or, more rarely, inconclusive.
Negative results for the antigen and toxins A and B indicate that C. difficile is probably not responsible for the symptoms reported by the patient. A positive result for the antigen and toxins A and B confirms that C. difficile is most likely responsible for the symptoms. A result that is positive for the antigen but negative for the toxins indicates that the bacteria is probably not responsible for the symptoms. However, since the toxin is relatively unstable, stability problems can cause false negative results for the toxins. If in doubt, the test may need to be repeated on a new specimen.