Diagnostic Approach for Toxin A Positive, Toxin B Negative Results

Verification and Clinical Assessment

• Request repeat testing or use an alternative testing platform to rule out technical error, as this result pattern is biologically implausible 1
• Consider using a multi-step algorithm (GDH plus toxin A/B EIA, or GDH plus toxin arbitrated by NAAT) rather than relying on a single test result 2, 3
• Assess for high-risk features including significant leukocytosis, rising serum creatinine, fever, or severe abdominal pain 4

Treatment Decision Algorithm

• Initiate empiric treatment with oral vancomycin 125 mg four times daily for 10 days while awaiting confirmatory testing, as severe illness warrants treatment before complete diagnostic workup 4
• Withhold antibiotics pending repeat or confirmatory testing using NAAT or cell cytotoxicity neutralization assay (CCNA) 2, 3
• Implement contact precautions regardless of treatment decision to prevent potential transmission 4

Key Considerations

• Avoid testing asymptomatic patients or those without diarrhea, as this detects colonization rather than infection 1, 5
• Do not repeat testing within 7 days of the initial test during the same diarrheal episode, as this increases false-positive results and has only 2% diagnostic yield 5