C. difficile Swab Testing
Yes, perirectal swabs can be used as an alternative to stool specimens for C. difficile testing, but only in specific clinical situations when patients cannot produce stool samples.
When Perirectal Swabs Are Appropriate
For patients with suspected severe C. difficile infection complicated by ileus who are unable to produce stool specimens, perirectal swabs provide an acceptable alternative with excellent diagnostic performance. 1
- Perirectal swab testing by PCR demonstrates 95.7% sensitivity, 100% specificity, 100% positive predictive value, and 99.1% negative predictive value compared to stool testing 1
- This approach is specifically recommended for selected patients who cannot provide stool samples due to ileus or severely disturbed bowel function 1
Standard Testing Approach: Stool Specimens Remain Preferred
Diagnostic testing should be performed only on unformed stool samples from symptomatic patients as the standard approach. 1, 2
- Testing should only be done on patients with ≥3 unformed stools in 24 hours with no obvious alternative explanation 3
- Stool specimens remain the gold standard sample type for C. difficile testing in most clinical scenarios 1
- Testing formed stool can result in false positive results and unnecessary antibiotic therapy 1
Key Clinical Pitfall to Avoid
Do not routinely use perirectal swabs as a substitute for stool testing in patients who can produce stool specimens. The evidence supporting perirectal swabs is limited to the specific scenario of ileus where stool collection is impossible 1. Using swabs inappropriately may alter test performance characteristics and lead to misdiagnosis.
Recommended Testing Algorithm
When perirectal swabs are used in appropriate patients (those with ileus), they should be tested using the same multi-step algorithms recommended for stool specimens 3:
- With pre-agreed institutional criteria for sample submission: Use NAAT alone or a multistep algorithm (GDH plus toxin; GDH plus toxin arbitrated by NAAT; or NAAT plus toxin) 3
- Without pre-agreed criteria: Use a stool toxin test as part of a multistep algorithm rather than NAAT alone 3
Clinical context including recent antibiotic exposure, hospitalization history, fever, abdominal pain, and leukocytosis should guide interpretation of results 1, 2