Clostridium difficile Toxin Assay
Test Description
Clostridium difficile is a gram-positive bacterium that is normally present in the
large intestine. When patients are taking broad-spectrum antibiotics, especially
ampicillin, cepalosporins, or clindamycin, the normal flora of the intestine are
diminished. However, C. difficile is resistant to these antibiotics, so its presence
actually increases under these circumstances. Its presence can also increase in
immunocompromised patients.
C. difficile releases two necrotizing toxins (A and B), one of which causes necrosis
of the lining of the colon. This results in the development of Pseudomembranous
colitis, a potentially fatal condition, 4 to 10 days after the antibiotic therapy is initiated.
Symptoms include complaints of abdominal cramping, fever, and copious
amounts of watery diarrhea. Leukocytosis is also present. Through testing for this
bacterial infection, treatment can be initiated, including discontinuance of the
broad-spectrum antibiotics, administration of metronidazole or vancomycin, and, if
needed, intravenous infusion of fluids.
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THE EVIDENCE FOR PRACTICE
Any illness involving diarrhea that persists for greater than 7 days, especially in an
immunocompromised patient, should prompt further testing of stool specimens.
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Normal Values
Negative
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Possible Meanings of Abnormal Values
Increased
• Antibiotic-related pseudomembranous enterocolitis
• C. difficile colitis
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Contributing Factors to Abnormal Values
• False negative may result if sample was not processed promptly or stored correctly
prior to processing.
• False positive may occur with grossly (visibly) bloody stool samples.
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Interventions/Implications
Pretest
• Explain to the patient the purpose of the test and the need for a stool sample to be collected.
• Instruct the patient to avoid contaminating the stool with toilet paper or urine. This can
be done through use of a plastic collection receptacle in the toilet.
• No fasting is required before the test.
Procedure
• Obtain a 5-mL stool specimen in a plastic screw-cap container.
• The specimen should be placed on ice or refrigerated.
• Gloves are worn when dealing with the specimen collection.
Posttest
• The sample is labeled and transported to the laboratory as soon as possible after collection
of the specimen.
• Report abnormal findings to the primary care provider.
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Clinical Alerts
• Due to the effect of the toxin on the colon lining, patients should be monitored
for signs/symptoms of colon perforation.
• Endoscopic evaluation of the colon may be useful for diagnosis.
• Due to its high cost, use of vancomycin may require preauthorization from the
patient’s insurance carrier for medication coverage.
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