Guideline Laboratory Detection of Toxigenic Clostridium difficile

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Highlights:

1. Testing for toxigenic C. difficile should be limited to patients with > 3 non­formed stool  specimens per 24 hr period, unless ileus (obstruction) is suspected.
2. Utilizing toxin A/B EIA for C. difficile diagnosis is insensitive and no longer recommended as a stand alone test.
3. Glutamate dehydrogenase (GDH) antigen assays have been found to be good screening tests for C. difficile infection (CDI) in many studies with high sensitivity and negative predictive values.
4. Positive GDH assay results must be confirmed. A GDH positive result along with a  positive toxin A/B EIA, a positive cytotoxin neutralization or a positive nucleic acid  amplification test (NAAT) result may be reported as positive for toxigenic C. difficile.  If the A/B EIA or cytotoxin neutralization assay is used and is negative, specimens should  be further tested by either NAAT or toxigenic culture.
5. Laboratories can also use a NAAT to detect C. difficile toxin genes as a stand alone diagnostic test.
6. Repeat testing following a positive test (test of cure) is not recommended since patients may carry toxigenic C. difficile for months after clinical cure. Repeat testing following a positive test is appropriate if the patient improves with therapy and relapses after the completion of a treatment regimen (clinical relapse).
7. Repeat testing following a negative test is not recommended if one of the suggested algorithms (see below) is used because nearly all positive patients will be detected (high sensitivity). Testing a second specimen from a negative patient is more likely to be a false ­positive. 
8. Up to 50% of neonates may be colonized with toxigenic C. difficile. Testing for C. difficile infection (CDI) in this population should proceed only after consultation with the clinician.