Do Not Repeat C. difficile Testing During Treatment
Do not repeat C. difficile toxin testing within 7 days during the same diarrheal episode in a patient already on treatment. 1
Why Repeat Testing is Not Recommended
The IDSA/SHEA guidelines provide a strong recommendation against repeat testing based on several key factors:
Minimal diagnostic yield: Repeat testing within 7 days yields positive results in only approximately 2% of cases, making it clinically unhelpful 1
Risk of false positives: Multiple repeat testing significantly increases the likelihood of generating false-positive results, particularly with highly sensitive tests like NAATs 1
High negative predictive value: Modern testing strategies (2-stage algorithms or stand-alone NAATs) have negative predictive values typically exceeding 99%, meaning a single negative test is highly reliable 1
No value for test of cure: More than 60% of patients remain C. difficile positive even after successful treatment, so testing to confirm cure is meaningless 1, 2
When to Consider Testing Again
There are only two specific scenarios where repeat testing may be appropriate:
After symptom resolution and recurrence: If diarrhea completely resolves with treatment but then recurs after stopping therapy, this represents a new episode requiring repeat testing (ideally including toxin detection, as 35% of recurrent diarrhea in CDI patients tests toxin-negative) 1
Epidemic settings with high clinical suspicion: During documented outbreaks where CDI acquisition is more frequent, repeat testing may have value in patients whose symptoms worsen despite initial negative results 1
Management During Treatment
Instead of repeat testing, focus on clinical assessment:
Monitor treatment response: Diarrhea and colitis typically improve within 3 days of starting appropriate therapy 1, 2
Assess for complications: Watch for signs of severe disease including significant leukocytosis (≥15,000 cells/mL), rising serum creatinine (>1.5 mg/dL), high fever, or severe abdominal pain 2, 3
Consider alternative diagnoses: If symptoms persist or worsen despite appropriate treatment, investigate other causes of diarrhea rather than reflexively retesting for C. difficile 3
Common Pitfall to Avoid
The most common error is ordering "test of cure" after treatment completion. This practice has no clinical utility and will mislead management, as toxigenic C. difficile commonly persists after successful treatment without causing disease 1, 2