Intestinal permeability ("leaky gut") test

ND-recommended test reviewed: intestinal permeability test (lactulose/mannitol urine or serum zonulin).
Indications reviewed: 'leaky gut', fatigue, food sensitivity; no validated indication identified.
Not ordered. Rationale discussed: 'leaky gut syndrome' not a recognized diagnosis; commercial zonulin assays shown not to detect the protein they claim to measure. Ref: Ajamian et al 2019, PLoS ONE.
Patient informed test available privately via ND. Patient given info page: https://labs.ajaxharwoodclinic.com/intestinal-permeability/patient
Revisit if: a specific, testable condition (e.g. celiac disease) is suspected on history or exam.

Indicated when

None recorded.

Not indicated when

• —Ordering a lactulose/mannitol urine test or a serum zonulin level to diagnose 'leaky gut syndrome' or to explain fatigue, food sensitivity, autoimmune disease, or other nonspecific symptoms, in any patient

Why not

'Leaky gut syndrome' is not a recognized medical diagnosis. For the serum zonulin assay specifically, a study using immunoprecipitation and mass spectrometry found that widely used commercial zonulin assays were not actually detecting zonulin at all: the antigens they detected were identified as haptoglobin and complement C3 instead, meaning 'current commercial zonulin assays are not detecting the actual protein' they are marketed to measure [1]. This calls into question any result and any treatment decision based on it.

Better first step

Investigate the actual symptoms or suspected condition directly (for example celiac serology for suspected celiac disease, or a structured elimination approach for suspected food-related symptoms) rather than testing intestinal permeability.

Typical ND rationale

An ND may order a lactulose/mannitol urine test or a zonulin blood level, reasoning that an overly permeable gut lining ('leaky gut') allows undigested food particles and toxins to enter the bloodstream and trigger inflammation, food sensitivities, or autoimmune activity, and that measuring permeability directly could confirm and help track this.

Ontario coverage & CONO orderability

OHIP status

unverified

Neither a lactulose/mannitol permeability test nor serum zonulin appears by name in the 2026 Schedule of Benefits for Laboratory Services (searched in full for 'permeability', 'lactulose', 'mannitol', and 'zonulin'), so billing status if a physician ordered one is unverified. ND-ordered testing is privately paid regardless (Reg. 552 s.22(1)).

CONO orderable

Yes — CONO list #193

CONO 193 'Intestinal permeability test' is listed with specimen 'breath' in the source CONO list, which appears to be a data-entry quirk: the standard lactulose/mannitol permeability test is a urine test, not a breath test, and a separate serum zonulin assay marketed for the same purpose is not separately listed on the CONO list.

Linked conditions

• dysbiosis ↗

Counselling script

“Intestinal permeability testing, including the zonulin blood test, isn't something I'd order, because researchers found the common commercial zonulin assays aren't actually measuring what they claim to measure, and 'leaky gut syndrome' itself isn't a recognized diagnosis. I'd rather look directly for what might be causing your symptoms, so the result actually tells us something we can act on.”

Revisit if

• —A specific, testable condition is suspected (e.g. celiac disease, IBD, food allergy)

References

1. [1]Monash University / The Alfred Hospital (Ajamian et al.) (2019). Serum zonulin as a marker of intestinal mucosal barrier function: May not be what it seems. linkCommercial zonulin assays were shown not to detect actual zonulin protein; detected antigens were identified as haptoglobin and complement C3
2. [2]Ontario Ministry of Health (2026). Ontario Health Insurance Plan: Schedule of Benefits for Laboratory Services (effective April 1, 2026). linkCommunity lab tests are insured only when ordered under the Schedule by an authorized prescriber
3. [3]Government of Ontario (e-Laws) (2026). Health Insurance Act, R.R.O. 1990, Reg. 552: General, s. 22 (insured laboratory services). linkInsured lab testing requires ordering by an authorized provider who has clinically assessed the patient
4. [4]Ontario Ministry of Health (2026). Ontario Health Insurance Plan: Schedule of Benefits for Laboratory Services (effective April 1, 2026). linkTests ordered by anyone other than an authorized provider, including NDs, are not insured services