Clostridium Difficile Toxin Test

Definition

The Clostridium difficile toxin test is a medical test that detects the existence of Clostridium difficile toxin A and B in a fresh or frozen stool (feces) sample.

Purpose

The bacterium Clostridium difficile, also known as C. difficile and C. diff, is an organism found in the intestines of humans. It is thought that up to 70% of healthy infants and 5% of healthy adults possess C. diff. This bacterium is also found in other animals. C. diff can live from months to years in the intestines without dying. Current medical research has not identified the length of time C. diff toxin can remain in the body before symptoms, such as abdominal pain or cramping, hard, tender, or swollen belly, fever, watery diarrhea, and vomiting, occur.

The purpose of this test is to detect the presence of Clostridium difficile in the intestine by testing for the toxins it releases which are eliminated in stool. The C. diff toxin test is used to help diagnose antibiotic-associated diarrhea and pseudomembranous colitis caused by C. diff. It may also be used to monitor the effectiveness of treatment and to detect a recurrence of colitis.

Precautions

The C. diff toxin is a common cause of diarrhea after antibiotic use because antibiotics weaken or kill many of the other bacteria in the intestine, allowing C. diff to multiply and strengthen. Therefore, this test should be performed when there is an indication that diarrhea is the result of recent antibiotic use. The patient should review all recent antibiotic use with the physician before taking this test. The test is not performed on children younger than one year of age. Proper storage of stool before testing is essential to achieve accurate test results.

Description

About three-quarters of C. difficile produce two toxins. Toxin A is an enterotoxin that binds to receptors in the bowel wall of the human mucosa. Toxin B is a cytotoxin for which a receptor has not yet been found in the human bowel mucosa.

C. diff is contagious. People are particularly vulnerable to infection when in hospitals, day care centers, and long-term care centers. In addition, people who have been previously infected by the bacterium or who have had recent chemotherapy or gastrointestinal surgery, are more susceptible to C. diff.

Under normal circumstances, C diff is just one of many types of bacteria that reside in the colon. As a group, these bacteria are described as normal flora. However, when other normal flora are weakened—for instance, during antibiotic treatment—C. diff may grow faster than normal. This faster growth rate often changes the bacterial balance, thus altering the normal flora. When overgrowth of C. diff occurs, prolonged acute diarrhea often occurs. Eventually, damage to the colon lining can develop, which can lead to pseudomembranous colitis.

There are two primary laboratory methods used to detect C. diff toxin. A cell cytotoxin assay is the traditional method. In this method, a stool specimen is incubated in the laboratory. Tissue culture cells are monitored for up to 48 hours until a result is obtained. A more modern method is called an enzyme immunoassay (EIA). The EIA method is faster and simpler than the cell cytotoxin assay. Results are generally obtained within one hour, but with a lower degree of accuracy provided by cytotoxin assay test.

Preparation

Samples are collected in various ways. The most convenient way is to catch the stool on plastic wrap that is positioned over the toilet bowl and held securely by the toilet seat. The sample should not contain any contaminates such as water, urine, or toilet tissue. For children wearing diapers, the diaper can be lined with plastic wrap.

In any method, a sample should be collected in a sterile, leak-proof container, which is securely closed after the sample is deposited, so that the sample has a minimal opportunity of being contaminated. The patient must pass at least three loose stools within 24 hours of the test before it can be performed. A minimum stool size should be 0.02 ounces (0.5 grams), which is similar to the size of a marble. The container is usually labeled with vital information such as the patient's name, date of birth, and date and time of the collection. The sample should be taken for analysis to a laboratory within three hours or should be refrigerated and taken to a laboratory as soon as possible. An inaccurate test may result if the sample is left at room temperature for more than four hours. The sample may be refrigerated up to 48 hours. It can be frozen (usually with dry ice) at a temperature of −4°F (−20°C) or lower if the likely delivery time to the laboratory is over 12 hours.

Aftercare

If the test comes back positive, the health care provider may eliminate antibiotic treatment or change to a different antibiotic treatment. C. diff can be treated with either metronidazole or vancomycin.

Complications

There are no known complications or risks associated with the C. diff toxin test. The severity of the disease can range from mild diarrhea to life-threatening colitis. Complications from the toxin, itself, can lead to serious illness or death, especially with people over 65 years of age.

Results

If the results of the C. diff toxin test come back positive, it is likely that the patient is experiencing symptoms caused by an excess of the C. diff toxin. If the test is negative, but symptoms continue, another sample should be taken. The C. diff toxin test is about 95% accurate with respect to sensitivity and specificity, so a repeat test is advisable to assure an accurate result. Another reason to repeat the test is the chance that the sample was not processed promptly or stored correctly prior to processing.

Health care team roles

The health care team should take precautions around C. diff patients because the toxin is very contagious. The team should wear protective attire such as gloves, gowns, and masks. They should be aware that the infected person could spread the toxin to others. If at the hospital, the patient should be placed in a private room. The patient can see visitors, but only when special health and safety precautions are carried out.

KEY TERMS

Antibiotic— A substance that weakens or destroys bacteria.

Bacterium— A single-celled microorganism that lives in the body of its host.

Colitis— An inflammation of the colon.

Colon— The large intestine.

Cytotoxin— A substance that is poisonous to cells.

Enterotoxin— A specific type of cytotoxin that is located in the cells of the intestinal mucosa.

Enzyme— A complex chemical produced by living cells that controls the speed of chemical reactions.

Immunoassay— A technique that measures the amount of antibodies in living tissue.

Mucosa— The moist lining in the body of a mammal found in passages that lead to the outside of the body.

Resources

BOOKS

MacFaddin, Jean F. Biochemical Tests for Identification of Medical Bacteria. Philadelphia: Lippincott Williams & Wilkins, 2000.

Shannon, Joyce Brennfleck, ed. Medical Tests Sourcebook: Basic Consumer Health Information about Medical Tests. Detroit: Omnigraphics, 1999.

Shtasel, Philip. Medical Tests and Diagnostic Procedures: A Patient's Guide to Just What the Doctor Ordered. New York: HarperPerennial, 1991.

OTHER

AllRefer.com, A.D.A.M., Inc., American Accreditation Health Care Commission. "Stool C. Difficile Toxin" November 4, 2003. 〈http://health.allrefer.com/health/stool-c-difficile-toxin-info.html#definition%3〉.

American Association for Clinical Chemistry. "Clostridium difficile toxin: The Test" May 6, 2005. 〈http://www.labtestsonline.org/understanding/analytes/cdiff/sources.html〉.