T5003 - C. DIFFICILE TOX-B TEST
A tissue culture assay for the detection of Clostridium difficile toxin B in fecal specimens.
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. The organism is an opportunistic anaerobic bacterium that grows in the intestine once the normal flora has been altered by antibiotics. Clostridium difficile produces two toxins, A and B. Toxin B, often referred to as the cytotoxin, is the toxin detected by the tissue culture assay. The C. DIFFICILE TOX-B TEST uses a tissue culture format to detect the presence of cytotoxic activity (cell rounding) in fecal specimens and confirms the identification of C. difficile toxin by using specific antitoxin. Reagents in the kit include toxin control, specific antitoxin, and diluent.
Features
- Highly sensitive
- Easy to perform
- Ready-to-use reagents
- No benchtop incubation step required
- Minimizes repeated testing of specimens containing high toxin levels
Further Information
Frequently Asked Questions
Q: Can I use fecal samples that have been diluted in the C. DIFFICILE TOX A/B II™ Diluent in the TOX-B TEST?
A: No, the Diluent used in the EIA kits makes the sample unsuitable for use in the tissue culture assay.
Q: Both my sample wells, sample + PBS and sample + Antitoxin, show a cytopathic effect . What does this mean?
A: Although this happens infrequently, it may mean that there is too much toxin present in the sample to be neutralized by the specific antitoxin. The sample will have to be diluted further and retested because the results cannot be reported as positive until specific neutralization is seen in the well containing the sample + Antitoxin. The TECHLAB® C. DIFFICILE TOX-B TEST uses high titered antitoxin to minimize the chances of this happening.
Q: We are doing an evaluation of the EIA and comparing it to the tissue culture assay. A reasonable number of samples are coming up positive in the tissue culture assay that were negative in the EIA. Our values for sensitivity are not what the kit insert predicts. Does this mean that the EIA is not a reasonable alternative?
A: In clinical studies, the TECHLAB® C. DIFFICILE TOX A/B II™ showed a 98-99% correlation with tissue culture. The tissue culture assay, however, is more sensitive than the EIAs, and you may be seeing some samples that are missed by your EIA. To minimize this from happening, use an EIA that detects both toxins, just in case you are dealing with a toxin A-negative, toxin B-positive isolate. An EIA that detects both toxins also will be more sensitive in detecting weakly positive samples. Even so, keep in mind that the tissue culture assay is not perfect. Make sure that your controls in the tissue culture assay are working properly and that you are not seeing nonspecific cytotoxic activity. Your results may be due to high levels of proteases found in some fecal samples. This protease activity can be neutralized non-specifically by the protein in the antibody well, making the result seem like a true C. difficile toxin positive sample. When there is doubt about a result in the tissue culture assay, use some neutral goat serum in one of the patient wells to determine whether the neutralization is specific.
Q: We have a sample that tested positive in a C. DIFFICILE toxin A test and negative in the C. DIFFICILE TOX-B TEST. Is this a toxin A positive, toxin B negative sample?
A: There has been only one report of a toxin A positive, toxin B negative isolate of C. difficile. This was from the feces of a horse. We have not seen this reported in humans. Remember that with the tissue culture test, the toxin must be biologically active. If the sample contained proteases that degraded the toxin or had been frozen and thawed multiple times, there is a chance that the tissue culture test would be negative and the EIA (which does not depend upon the intact toxin being present for detection) was positive. PCR using primers specific for the toxin genes could be used to get a definitive answer.
Q: We have a sample that tested negative in a C. DIFFICILE toxin A test and positive in the C. DIFFICILE TOX-B TEST. Is this a toxin A negative, toxin B positive sample?
A: Perhaps. There are a number of reports of toxin A negative/toxin B positive clinical isolates. These isolates are associated with clinical disease and they have been reported to cause the death of some patients. Therefore, it is important that these isolates are not missed in clinical testing. Keep in mind that the tissue culture assay is extremely sensitive. It is the gold standard and detects toxin B at picogram levels, making it more sensitive than the EIA for toxin A. The negative toxin A EIA result may only mean that the level of toxin A in this particular sample was too low to be detected by the EIA. The only way to confirm whether it is a toxin B positive, toxin A negative sample would be to use either the C. DIFFICILE TOX A/B II™ or culture and PCR.
Q: What is the CPT code for the C. DIFFICILE TOX-B TEST?
A: The CPT code is 87230.