- Testing for toxigenic C. difficile should be limited to patients with > 3 nonformed stool specimens per 24 hr period, unless ileus (obstruction) is suspected.
- Utilizing toxin A/B EIA for C. difficile diagnosis is insensitive and no longer recommended as a stand alone test.
- 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.
- 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.
- Laboratories can also use a NAAT to detect C. difficile toxin genes as a stand alone diagnostic test.
- 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).
- 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.
- 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.
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