Update on the Laboratory Diagnosis of Clostridium difficile Infection
Published: September 2012
Hot Topic Q&A is an opportunity for viewers to submit questions to the Hot Topic presenter. The opportunity to submit questions for this topic is now closed.
The following questions were submitted by viewers and answered by the presenter, Jon Rosenblatt, MD, a Professor of Medicine and Microbiology at Mayo Clinic, as well as a consultant in the Division of Clinical Microbiology.
Questions are presented as submitted (unedited).
How sensitive is the Clostridium difficile glutamate dehydrogenase (GDH) antigen screening assay?
The GDH screening assay by itself has a sensitivity of 90%-100% for the detection of all C difficile but it detects both toxigenic and non-toxigenic strains, so it has a lower specificity for detecting strains that cause C difficile infection.
If you can guide briefly about how to collect samples for Clostridium difficile testing and how to order the test it will be very helpful.
The most important factors in collection are to make sure the patient actually has diarrhea and the specimen is liquid. Ordering and collection devices will depend upon which test is being done and what the manufacturer specifies. Mayo Medical Laboratories requirements can be found at www.MayoMedicalLaboratories.com in the test catalogue section.
If the Wampole C. diff Quick Check Complete (a rapid membrane enzyme immunoassay for the detection of CDI) is positive, can a positive result for CDI be assumed? It detects both GDH antigen and toxins A and B in fecal specimens.
If both tests are positive, then that is presumptive evidence for the presence of toxigenic C difficile.
Does a positive toxin result need to be confirmed by PCR?
Do you limit the number of tests for negatives (how long before they test) or is it when a new episode begins?
Because we routinely perform a sensitive PCR method, we do not recommend further testing after 1 negative specimen. We will not reject a second specimen but if more than 2 are ordered within 3 to 4 days, we will contact the physician to discourage further testing.