What does the Clostridioides difficile Toxin B (Cytotoxin) test measure?

Why is Clostridioides difficile Toxin B (Cytotoxin) measured?

Toxin B detection is clinically the more sensitive and critical toxin target in C. difficile diagnostics. Its presence in stool from a symptomatic patient with clinically significant diarrhoea confirms active toxin-mediated colonic injury. Detection of Toxin B in the absence of Toxin A — occurring in approximately 3–5% of toxigenic C. difficile strains — would be missed by Toxin A-only assays, supporting the clinical rationale for combined A&B testing. In the context of EIA-based testing, a positive Toxin B result alongside or without Toxin A has high specificity for CDI and supports treatment initiation per IDSA/SHEA guidelines.

Reference ranges

Standard reference

Negative (not detected) # REVIEWER FLAG: Confirm discrete vs combined Toxin A&B reporting format with Access Medical Laboratories — see note above for Toxin A.

Functional medicine optimal

Not applicable — qualitative assay; negative is the expected result in appropriately tested individuals.

Units

Qualitative (Positive / Negative)

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.