What does the Zonulin (Faecal), by immunoassay test measure?

Why is Zonulin (Faecal), by immunoassay measured?

Faecal zonulin is offered as a marker of intestinal permeability and is ordered in functional and integrative practice to characterise barrier function, most often in patients with gastrointestinal symptoms, autoimmune disease, or food sensitivity. The evidence does not currently support this application. Independent analytical work using mass spectrometry found that widely used commercial zonulin immunoassays do not detect pre-haptoglobin-2 and instead cross-react with other structurally unrelated proteins, and different commercial kits yield poorly correlated results on the same specimens. Correlation with direct permeability measures such as the lactulose-mannitol ratio is inconsistent. Zonulin should therefore be regarded as an exploratory research measure rather than a validated clinical test, and should not be used to diagnose a condition or direct treatment.

Reference ranges

Standard reference

Reported against the laboratory's own reference population; no standardised or validated reference interval exists, and values are not comparable between commercial assays

Functional medicine optimal

Not applicable — no validated optimal or target value exists, and the measure is not established as a basis for intervention

Units

ng/mL, ng/g

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