Stool Specimen Collection for Clostridioides difficile Testing
Only collect unformed (liquid or soft) stool specimens from patients with ≥3 unformed stools in 24 hours who have no obvious alternative explanation for diarrhea, and do not collect specimens from patients who have received laxatives within the previous 48 hours. 1
Patient Selection Criteria for Specimen Collection
Who should have specimens collected:
- Patients with unexplained new-onset diarrhea defined as ≥3 unformed stools in 24 hours 1, 2
- Patients with healthcare-associated diarrhea regardless of antibiotic exposure 2
- Community patients with persistent diarrhea after negative testing for common enteropathogens 3, 4
- Patients with recent antibiotic use (within 4-6 weeks), chemotherapy exposure, or hospitalization 2, 4
Who should NOT have specimens collected:
- Patients receiving laxatives within the previous 24-48 hours 1, 4
- Asymptomatic patients (except for epidemiological studies) 1
- Neonates or infants ≤12 months of age with diarrhea, due to high asymptomatic carriage rates 1
- Patients with formed stool, as this leads to false positives and unnecessary treatment 5, 4
Specimen Type and Collection Method
Standard collection approach:
- Collect only unformed (liquid or soft) stool that takes the shape of the container 5, 1
- Laboratories should reject formed stool specimens to improve test specificity 1
- A single diarrheal stool specimen is typically sufficient for initial testing 1
Alternative for patients with ileus:
- For patients with suspected severe CDI complicated by ileus who cannot produce stool specimens, perirectal swabs tested by PCR provide an acceptable alternative with sensitivity of 95.7%, specificity of 100%, and negative predictive value of 99.1% 5
- This approach is specifically recommended for surgical patients or those with signs of severely disturbed bowel function 5
Critical Collection Pitfalls to Avoid
Common errors that compromise diagnostic accuracy:
- Testing patients on laxatives or promotility drugs, which creates false clinical presentations 1
- Collecting formed stool specimens, which detects asymptomatic colonization rather than active infection 5, 4
- Repeat testing within 7 days during the same diarrheal episode, which is not recommended and wastes resources 1
- Testing for "test of cure" in asymptomatic patients after treatment, which is never indicated 1
Institutional Coordination for Appropriate Specimen Submission
Healthcare facilities should establish preagreed criteria:
- Clinicians and laboratory personnel should agree institutionally to submit specimens only from patients meeting clinical criteria (≥3 unformed stools in 24 hours, no laxatives) 1
- Some institutions use electronic medical record forms requiring providers to document frequency and consistency of bowel movements before testing is performed 6
- Empowering healthcare workers collecting specimens to discuss stool consistency with clinicians reduces inappropriate testing 6
- Laboratories can collaborate with infection prevention and antibiotic stewardship teams to periodically audit appropriateness of testing through chart review 1
Age-Specific Considerations
Pediatric patients:
- Never routinely test neonates or infants ≤12 months of age due to high prevalence of asymptomatic carriage (strong recommendation) 1
- For children >12 months, use the same criteria as adults: ≥3 unformed stools in 24 hours with no alternative explanation 1
Community-acquired cases:
- Community-acquired CDI occurs across all age ranges (1-92 years), with 18% of cases under age 20 3, 4
- Do not exclude testing based on absence of traditional risk factors, as 25-26% of community cases lack healthcare exposure or recent antibiotics 3, 4