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C. difficile GDH/Toxins A and B
Test CodeCDIFFGDH
Alias/See Also
C. difficile GDH Antigen and Toxins A and B
Preferred Specimen
Stool, Liquid. 5 mL unpreserved liquid or soft stool in a sterile container (1 mL min). Stool sample must be of a consistency to conform to the shape of the container.
Instructions
Send specimen to laboratory as soon as possible, preferably within two hours.
For Patients <2 years old: Consider cancelling the test because of the high colonization rates in infants and children under 2 years of age. The rate of intestinal colonization of cytotoxin-producing C. difficile in healthy neonates has been reported as high as 50%. Patients 32 to 365 days old: Results for children of 2-12 months should be interpreted with caution due to the high carriage rate (<5%) of cytotoxin-producing C. difficile in healthy members of this age group. The asymptomatic state within this population has been associated with reduced expression of the toxin binding receptor on colonic epithelial cells and the presence of immunoglobulin from human milk.
For patients receiving laxatives:
Do NOT test patients who have been on any laxatives in prior 48 hours unless clinical suspicion for CDAD is high.
INTERPRETING RESULTS:
Negative GDH with Negative Toxins A/B: No indication of Clostridioides (formerly Clostridium) difficile-associated diarrhea (CDAD) and no colonization.
Positive GDH with Positive Toxins A/B: Confirms Clostridioides difficile-associated diarrhea (CDAD). Isolate patient and treat according to Banner C. difficile Prevention and Management Consensus Guidelines.
Positive GDH with Negative Toxins A/B: C difficile present but toxin not detected. Indicates colonization with non-toxigenic strain or level of toxin below detectable levels. Isolate patient if diarrhea (≥3 stools per day) present. Follow Banner C. difficile Prevention and Management Consensus Guidelines.
For Patients <2 years old: Consider cancelling the test because of the high colonization rates in infants and children under 2 years of age. The rate of intestinal colonization of cytotoxin-producing C. difficile in healthy neonates has been reported as high as 50%. Patients 32 to 365 days old: Results for children of 2-12 months should be interpreted with caution due to the high carriage rate (<5%) of cytotoxin-producing C. difficile in healthy members of this age group. The asymptomatic state within this population has been associated with reduced expression of the toxin binding receptor on colonic epithelial cells and the presence of immunoglobulin from human milk.
For patients receiving laxatives:
Do NOT test patients who have been on any laxatives in prior 48 hours unless clinical suspicion for CDAD is high.
INTERPRETING RESULTS:
Negative GDH with Negative Toxins A/B: No indication of Clostridioides (formerly Clostridium) difficile-associated diarrhea (CDAD) and no colonization.
Positive GDH with Positive Toxins A/B: Confirms Clostridioides difficile-associated diarrhea (CDAD). Isolate patient and treat according to Banner C. difficile Prevention and Management Consensus Guidelines.
Positive GDH with Negative Toxins A/B: C difficile present but toxin not detected. Indicates colonization with non-toxigenic strain or level of toxin below detectable levels. Isolate patient if diarrhea (≥3 stools per day) present. Follow Banner C. difficile Prevention and Management Consensus Guidelines.
Negative GDH with Positive Toxins A/B: CDAD not confirmed, but highly suspicious. High antibody production against antigen in relapsing patients may bind GDH and cause nonreactive result with a reactive toxins AB result. Isolate patient and resubmit a fresh loose-stool specimen. If second specimen result is same – consider as CDAD (relapse). Continue patient isolation and treat according to Banner C. difficile Prevention and Management Consensus Guidelines.
Transport Container
Clean, leak-proof containers
Specimen Stability
Refrigerated: 72 hours
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
- Formed stool
- Fecal specimens in Formalin-based fixative (e.g. sodium acetate formalin, 10% formalin, merthiolate formalin)
- Fecal specimens in alcohol-based fixative (e.g. polyvinyl alcohol)
Methodology
Qualitative Rapid Membrane Enzyme Immunoassay
For GDH, published sensitivity of the assay is 98.7% compared to cytotoxicity testing. For Toxin AB, the published sensitivity is 87.8% and specificity 99.4% compared to cytotoxicity testing.
Setup Schedule
Routine
Report Available
Qualitative Rapid Membrane Enzyme Immunoassay: <12 hours
Reference Range
Normal=Not Detected
Clinical Significance
NOTE: The clinical determination of CDAD should not be determined solely on the C. difficile multistep algorithm but should include both the clinical history and presentation of the patient (i.e., recent exposure to antibiotics, ≥3 unformed stools per day, leukocytosis, etc.).
