Clostridium difficile toxin
At a Glance
Why Get Tested?
To detect the presence of Clostridium difficile toxin
When to Get Tested?
When a patient has acute diarrhoea that persists for several days, abdominal pain, fever, and/or nausea following antibiotic therapy.
Sample Required?
A fresh stool sample that has not been contaminated with urine or water
The Test Sample
What is being tested?
This test detects the presence of Clostridium difficile toxin A and/or B in a fresh or frozen stool sample. C. difficile is a bacterium that is present in the intestines of up to 70% of healthy infants and 5% of healthy adults. C. difficile is one of the groups of bacteria that usually inhabit the colon and as such are called “normal flora.” If something happens to depress the growth of the other normal flora, such as broad-spectrum antibiotic therapy, C. difficile may overgrow and disrupt the balance of bacteria in the colon. About 75% of C. difficile produce two toxins, A and B. The combination of overgrowth and toxin production can cause prolonged acute diarrhoea and the toxin can damage the lining of the colon and lead to pseudomembranous colitis, a severe inflammation of the colon.
C. difficile is the major cause of antibiotic-associated diarrhoea in the hospital, affecting as many as 20% of those who are taking antibiotics for other infections. While C. difficile is frequently carried by infants, it does not usually cause diarrhoea in this population. The risk of being affected increases with age and is increased in those who are immunocompromised, have acute or chronic colon conditions, have been previously affected by C. difficile, or who have had recent gastrointestinal surgery or chemotherapy. About 80% of the time, C. difficile-associated diarrhoea occurs in patients who have been taking antibiotics for several days, but it can also occur several weeks after treatment is completed.
The severity of C. difficile diarrhoea and colitis may vary greatly ranging from mild diarrhoea to a more severe colitis, or to toxic megacolon, which can result in sepsis and death.. Symptoms may include frequent loose stools, abdominal pain and cramps, nausea, fever, dehydration, and fatigue. Patients may have blood, mucous, or white blood cells (WBCs) in their stool and frequently have leucocytes (increased numbers of WBCs in their blood). While some cases of C. difficile diarrhoea and colitis do not require treatment, others require specific oral antibiotic therapy. Most patients improve as the normal flora re-establishes itself, but about 20% of patients may have one or more relapses, with symptoms and detectible toxin levels re-emerging.
How is the sample collected for testing?
A fresh stool sample is collected in a sterile universal container. The stool sample should not be contaminated with urine or water. Once it has been collected, the stool should be taken to the laboratory as soon as possible, or stored in a designated refridgerator if there is to be delay. The container should be labelled with the patient’s name and the date and time of the stool collection.
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Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
The Test
How is it used?
The Clostridium difficile toxin test is used to diagnose antibiotic-associated diarrhoea and pseudomembranous colitis that is caused by C. difficile. It may also be requested to monitor the effectiveness of treatment for C. difficile diarrhoea and to detect a recurrence. Although it is possible to detect the presence of C. difficile by growing the bacteria (stool culture), the results of the culture take several days and further testing must be done to detect the toxin.
When is it requested?
A C. difficile toxin test may be requested when a patient in hospital has frequent loose stools, abdominal pain, fever, and/or nausea during or following a course of antibiotics or following a recent gastrointestinal surgery. It may be requested when an outpatient develops these symptoms within 6-8 weeks after taking antibiotics, several days after chemotherapy, or when a patient has a chronic gastrointestinal disorder that the doctor suspects is being exacerbated by a C. difficile infection. The C. difficile toxin test may be requested to help diagnose the cause of frequent diarrhoea when a patient has leucocytes and/or blood in the stool and no other discernable cause (such as parasites or other pathogenic bacteria) has been detected.
If a patient treated for antibiotic-associated diarrhoea or colitis relapses and symptoms re-emerge, C. difficile toxin testing may be requested to confirm the presence of the toxin.
What does the test result mean?
If the C. difficile toxin test is positive, it is likely that the patient’s diarrhoea and other symptoms are being caused by an overgrowth of toxin producing C. difficile. Occasionally, false positives may be seen with grossly (visibly) bloody stool samples.
If the test is negative but the diarrhoea continues, another sample needs to be tested. The C. difficile toxin test does not detect 100% of cases and the toxin may have been missed the first time. Since the toxin breaks down at room temperature, a negative result may also indicate that the sample was not processed promptly or stored correctly prior to processing. A negative test result may also mean that the diarrhoea and other symptoms are being caused by something other than C. difficile.
Is there anything else I should know?
Clostridium difficile can be grown and isolated on a stool culture, but its presence does not indicate whether the strain present is a toxin producer. It also does not distinguish between C. difficile colonization (presence in healthy individuals) and overgrowth/infection. The usual method to detect C. difficile toxin A and B is by a rapid enzyme immunoassay. Results are available after 1-4 hr depending on the test. A cytotoxin test that looks for the toxic effects of stool on human cells grown in culture is a more sensitive method to detect toxin, but it requires 24-48 hr to get the result.
An endoscopic procedure can be used to diagnose C. difficile colitis. A specialist (gastroenterologist) can observe and biopsy any characteristic pseudomembranous lesions that may be present.
Common Questions
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Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
