What does the Escherichia coli antigen test measure?

Why is Escherichia coli antigen measured?

A positive E. coli EIA indicates the presence of E. coli antigens in stool and may prompt further characterisation to identify the pathotype, particularly in cases of bloody diarrhoea (where EHEC and Shiga toxin testing are critical) or travellers' diarrhoea (commonly ETEC). Because commensal E. coli are ubiquitous in faeces, a positive qualitative screen must be interpreted alongside clinical presentation, stool characteristics, and complementary culture or molecular assays that discriminate pathogenic from non-pathogenic strains.

Reference ranges

Standard reference

Negative; OD ratio <1.0 (method-specific threshold).

Functional medicine optimal

Negative. Asymptomatic carriage of commensal E. coli is universal; the test is informative only in symptomatic patients or outbreak settings where pathogenic strains are suspected.

Units

Qualitative (Positive/Negative), Optical density (OD) ratio

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