T5025 - C. DIFF CHEK™ -60
An enzyme immunoassay for the detection of glutamate dehydrogenase (GDH) produced by both toxigenic and non-toxigenic strains of Clostridium difficile.
After treatment with antibiotics, many patients develop gastrointestinal problems ranging from mild diarrhea to severe pseudomembranous colitis. Many cases of the milder forms of gastrointestinal illness and most cases of pseudomembranous colitis are caused by Clostridium difficile, an opportunistic anaerobic bacterium that grows in the intestine once the normal flora has been altered by antibiotics. Toxigenic strains of C. difficile carry the genes encoding the toxins whereas non-toxigenic strains do not carry the toxin genes. The disease results from the toxins that the organism produces. The clinical symptoms associated with the disease are believed to be primarily due to toxin A, which is a tissue-damaging enterotoxin. C. difficile also produces a second toxin, designated toxin B. Toxin B, which has been referred to as the cytotoxin of the organism, is the toxin detected by the tissue culture assay currently used by many laboratories. Toxigenic C. difficile strains produce both toxins or only toxin B. The glutamate dehydrogenase (GDH) of C. difficile is a good antigen marker for the organism in feces because it is produced in high amounts by all strains, toxigenic or non-toxigenic. The antigen can be detected in fecal specimens by using the C. DIFF CHEK™ -60 test. A positive result in the test, which is highly specific for the glutamate dehydrogenase of C. difficile, confirms the presence of this organism in a fecal specimen; a negative result indicates the absence of the organism. A positive result should be followed by a toxin-specific test to confirm the presence of toxigenic C. difficile.
Features
- Easy to perform
- Results in an hour
- Sensitivity >99%
- Ideal screening test for facilities performing tissue culture
Further Information
Package Insert Issued 8/06
CPT Codes Issued 3/08
Material Safety Data Sheet Issued 6/06
Poster Presentation
C. DIFF CHEK™ -60: A Rapid and Cost Effective Method for Detection of Clostridium difficile in Fecal Specimens
Clinical Virology meeting, 2006, Clearwater, FL
Poster Presentation
Performance of TECHLAB® C. DIFF CHEK™ in Combination with C. DIFFICILE TOX A/B II™, Triage® C. difficile Panels, and a Cytotoxin Assay for the Diagnosis of C. difficile-Associated Diarrhea (CDAD)
American Society of Microbiology meeting, May 2004, New Orleans, LA
Poster Presentation
Evaluation of C. DIFF CHEK™, a Screening Test for Clostridium difficile
American Society of Microbiology meeting, May 2004, New Orleans, LA
Poster Presentation
Comparison of Screening Tests for Detection of Clostridium difficile in Fecal Specimens
American Society of Microbiology meeting, May 2004, New Orleans, LA
Poster Presentation
Evaluation of an Enzyme Immunoassay for Detection of the Clostridium difficile Common Antigen, Glutamate Dehydrogenase (GDH), in Fecal Specimens.
American Society of Microbiology meeting, May 2003, Washington DC
Poster Presentation
Evaluation of a Screening Test for Detection of Clostridium difficile in Fecal Specimens.
American Society of Microbiology meeting, May 2003, Washington DC
Poster Presentation
Evaluation of the TECHLAB® C. DIFF CHEK™-30 and C. DIFF CHEK™-60 for Detection of C. difficile in Fecal Specimens.
American Society of Microbiology meeting, May 2003, Washington DC
Frequently Asked Questions
Q: What does C. DIFF CHEK™ detect? What is the utility of this test?
A: C. DIFF CHEK™ detects a protein that is produced in large amounts by all strains of Clostridium difficile. This "common antigen" is the enzyme, glutamate dehydrogenase. Almost all species of bacteria produce glutamate dehydrogenase enzymes so the trick is to detect the specific C. difficile enzyme by using monoclonal antibodies (some other tests for the "common antigen" use antibodies that cross react with the enzyme from other species). Our test is extremely specific and very sensitive - it detects the presence of even relatively small numbers of cells of either toxigenic or non-toxigenic strains of C. difficile in feces. In most hospitals about 80% of the C. difficile strains produce toxins and a single patient may have multiple strains.
This test is especially useful when tissue culture is used as the toxin detection assay. By use of the C. DIFF CHEK™ the feces that do not contain C. difficile are reported as negatives in about an hour and this reduces the number of samples that need to be tested with the more time-consuming tissue culture assay by about 70%. The test also raises a caution flag for those patients that have organisms present but no toxin - the C. DIFF CHEK™ can detect the presence of organisms before there are enough cells present to produce detectable toxin.
Q: Can I use the C. DIFF CHEK™ test alone as the diagnostic aid for C. difficile disease?
A: C. difficile toxins are responsible for C. difficile disease. A positive test result by C. DIFF CHEK™ quickly indicates the presence of C. difficile, however, it does not distinguish toxigenic strains from non-toxigenic strains. A toxin test, either an EIA or a tissue culture assay should be used to confirm the presence of toxin in the fecal specimen. Patients colonized with non-toxic strains are susceptible to colonization with toxic strains so colonized patients should be watched closely for the appearance of toxins. Patients also may have very low amounts of toxin that cannot be picked up with the toxin assays at the stage of the disease development, yet the GDH level is high enough to be detected. The C. DIFF CHEK™ may detect the presence of these small numbers of cells - a positive result with this test is a caution flag.
Q: Does the C. DIFF CHEK™ test detect non-toxigenic strains of C. difficile?
A: Yes. C. DIFF CHEK™ detects the C. difficile "common antigen" which is the enzyme glutamate dehydrogenase. This enzyme is expressed at a high level in all strains of C. difficile, which makes the test very sensitive for the presence of the organism. But this test does not distinguish toxigenic strains of C. difficile from non-toxigenic strains.
Q: Is C. DIFF CHEK™ different from toxin ELISAs?
A: Yes. C. DIFF CHEK™ is more similar to culture in that it detects the presence of the organism rather than detecting the toxins. The toxin ELISAs detect Toxin A and/or Toxin B of C. difficile. Because about 20% of C. difficile isolates do not express the toxins, and all C. difficile express glutamate dehydrogenase at high levels, you will get samples that are positive in the C. DIFF CHEK™ but negative in ELISAs for the toxins.
Q: I'm satisfied with my toxin A/B EIA. Should I switch to the C. DIFF CHEK™ test?
A: No, you should not switch to the C. DIFF CHEK™ test if you are using a toxin A/B EIA. However, under optimal circumstances, laboratories that are currently using toxin EIAs may use C. DIFF CHEK™ for screening the samples first, or to use C. DIFF CHEK™ and a toxin EIA simultaneously. The discrepant samples would suggest that the patients would need to be monitored for possible development of the C. difficile disease, because these patients may have a very low expression of toxins. Alternatively these patients may carry non-toxigenic C. difficile, so the colon condition is suitable for toxigenic C. difficile to grow as well. We believe that such approach would provide better diagnosis in general, but the cost might be prohibitive.
Q: Is it cost effective to use C. DIFF CHEK™?
A: The answer depends on the current test you are using. If you are using a tissue culture assay C. DIFF CHEK™ reduces your workload by screening out about 75% to 80% of the samples, and thus is cost effective. In other words, if you test 100 samples using C. DIFF CHEK™, only about 25 to 30 will be positive and need to be further tested by tissue culture assay. You do not have to wait for the tissue culture results before reporting the 75 to 80 samples as negative. You may report the negative results in about an hour and report a "caution" for the remaining 25 to 30. The quick determination of the negative results may reduce unnecessary patient isolation and preventive measurements that are costly.
If you are using an expensive toxin EIA, it might be economically feasible to use the C. DIFF CHEK™ screen test first and test only the positive samples using your toxin EIA.
Q: What is the detection limit for the C. DIFF CHEK™?
A: The C. DIFF CHEK™ test detects C. difficile glutamate dehydrogenase at levels = 0.8 ng/mL. Large amounts of this enzyme are produced by all strains so the C. DIFF CHEK™ test is very sensitive for detecting the presence of C. difficile. Also, toxigenic strains vary greatly in the amounts of toxins produced so the C. DIFF CHEK™ can be positive earlier in an infection than the toxin tests.
Q: How long can I store a fecal sample before being tested in the C. DIFF CHEK™?
A: Undiluted fecal samples can be stored up to 72 hours between 2° and 8°C. Once the sample is diluted into the Diluent, it should be tested right away.
Q: Can I test fecal samples collected from barium enemas or colonic washings?
A: The test is not designed to be used on anything other than diarrheal fecal samples. If other types of sample are tested, the results reported to the physician should contain a disclaimer.
Q: Can I test solid samples?
A: We do not recommend testing solid samples; however, it is difficult to refuse to test a sample based on its consistency. If the lab decides to run the test be aware that this type of sample may give a false positive if the plate is not washed correctly or too much sample is used in the test. Take special care in washing the wells so that you remove any sticky material.
Q: Should I test samples from infants?
A: Despite the fact that 50% of infants in some hospitals carry C. difficile as normal flora, we recommend testing if symptoms consistent with C. difficile disease are present. C. difficile disease is primarily an opportunistic infection in the elderly population, but in rare instances, infants can acquire the disease. The physician should be advised about normal carriage rates in this population when the result is reported.
Q: How many times should a patient be tested?
A: The number of times a patient is tested varies from lab to lab. Some clinicians request a single test whereas others test patients throughout their hospital stay. In our opinion, if a patient's feces tests negative but the patient continues to be symptomatic, additional tests should be performed. If a sample is positive by C. DIFF CHEK™ yet negative with a toxin test, the patient should be monitored closely using additional toxin tests for the possibility of developing C. difficile disease.
Q: Can I use fecal samples that have been diluted in the C. DIFFICILE TOX-A TEST or C. DIFFICILE TOX A/B II™ Diluent in the C. DIFF CHEK™ test?
A: No, the Diluent used in the other EIA kits is different from the one in the C. DIFF CHEK™ test. Also do NOT mix reagents from lot to lot.
Q: We are doing an evaluation of the C. DIFF CHEK™ and comparing it to the tissue culture assay. A number of samples are coming up positive in the C. DIFF CHEK™ assay that are negative in the tissue culture assay. Does this mean that the C. DIFF CHEK™ is generating false positives?
A: In clinical studies, the TECHLAB® C. DIFF CHEK™ showed a 98-99% correlation with PCR-revised bacterial culture assay. This test detects both toxigenic and non-toxigenic strains of C. difficile while the tissue culture assay detects the toxin. The C. DIFF CHEK™-positive /tissue culture negative samples may have non-toxigenic strains of C. difficile. Alternatively, the sample may have very low levels of toxins that cannot be detected even when tissue culture assay is used. Keep in mind that glutamate dehydrogenase is expressed by some strains at a much higher level than the toxins. In a normal clinical laboratory about 20% of the fecal samples that contain C. difficile only have non-toxigenic strains and thus are negative on the tissue culture assay (or EIA for toxins).
Q: What is the CPT code for the C. DIFF CHEK™?
A: According to the 2006 coding, the CPT code is 87324.