Celiac serology (tTG-IgA + total IgA)

Pick Ordered or Not ordered to see the note.

Indicated when

• —Persistent GI symptoms (diarrhea, bloating, abdominal pain), unexplained iron-deficiency anemia, unexplained weight loss, or failure to thrive, in a patient currently eating gluten [1, 4]
• —First-degree relative with celiac disease, or a condition associated with higher celiac prevalence (type 1 diabetes, autoimmune thyroid disease, Down syndrome), even without classic GI symptoms
• —As part of the standard work-up when investigating irritable-bowel-type symptoms, per CAG's IBS guideline, which suggests serological testing to exclude celiac disease [2]

Not indicated when

• —Testing endomysial antibody (EMA), gliadin antibodies (IgG/IgA), or anti-reticulin antibodies as the initial screen for celiac disease: Choosing Wisely Canada specifically recommends against tTG-IgG or deamidated gliadin peptide (DGP) antibody testing for initial screening [3]; tTG-IgA plus total IgA is the correct initial pair
• —Testing after the patient has already started a gluten-free diet without a confirmed diagnosis, since antibody levels fall on a gluten-free diet and can produce a falsely reassuring negative result

Why not

When ordered correctly (tTG-IgA with total IgA, on a gluten-containing diet), celiac serology is accurate and low-risk; the main harms come from ordering the wrong initial panel (older antibody tests such as gliadin or anti-reticulin antibodies have largely been superseded, per Choosing Wisely Canada) or from testing after gluten has already been withdrawn, which can produce a false negative and either miss the diagnosis or require a prolonged gluten challenge to retest accurately.

Better first step

Order tTG-IgA with a total IgA level while the patient is still eating gluten; if IgA-deficient, use an IgG-based celiac antibody test instead. A positive result should lead to referral for confirmatory duodenal biopsy in most patients [1].

Typical ND rationale

An ND may order celiac serology in a patient with GI symptoms, fatigue, or a family history of celiac disease, reasoning that celiac disease is underdiagnosed, has a wide range of presentations beyond classic GI symptoms, and is readily missed if not specifically tested for.

Ontario coverage & CONO orderability

OHIP status

insured_conditional

Two tests are insured for the diagnosis of celiac disease under the 2026 Schedule: L570 Celiac tTG-IgA (fee $17.50) and L571 Celiac serum IgA (fee $1.50), only for patients over 2 years of age who are on a gluten-containing diet (Essential Specifications paragraph 21.1). L571 is only insured when medically necessary to confirm IgA deficiency and when L570 is billed for the same service. Older antibody tests (endomysial, gliadin, anti-reticulin) are not part of this insured pairing, and Choosing Wisely Canada recommends against using them for initial screening [3]. Insured only when a physician, midwife, or NP orders it; ND-ordered testing is patient-paid regardless (Reg. 552 s.22(1)).

CONO orderable

Yes — CONO list #124, #16, #56, #69, #22

CONO 124 'Transglutaminase IgA Antibody' and CONO 16 'Antibody Screening IgA' are the current, correct pairing. CONO 56 'Endomysial Antibody', CONO 69 'Gliadin Antibodies (IgG, IgA)' and CONO 22 'Anti-Reticulin Antibodies' are older test types still on the CONO list and included as aliases, but Choosing Wisely Canada recommends against using them for initial screening [3].

Linked conditions

• Celiac disease ↗
• Non-celiac gluten/wheat sensitivity (NCGS) ↗
• tired ↗

Counselling script

“Celiac disease is often missed, and this blood test is the right first test whenever there's a reason to suspect it, including tiredness or low iron without gut symptoms. The one thing that matters is that you're still eating gluten when the blood is drawn, otherwise the result can look falsely normal.”

Revisit if

• —New or worsening GI symptoms
• —Unexplained iron-deficiency anemia or weight loss
• —New relevant family history
• —Patient has already started a gluten-free diet before testing (discuss a supervised gluten challenge)

References

1. [1]American College of Gastroenterology (2023). American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease. linkACG guideline: CD-specific antibody detection (e.g. tissue transglutaminase) in serum is very helpful for initial screening; biopsy confirms diagnosis in most patients
2. [2]Canadian Association of Gastroenterology (2019). Canadian Association of Gastroenterology Clinical Practice Guideline for the Management of Irritable Bowel Syndrome (IBS). linkCAG IBS guideline: serological testing is suggested to exclude celiac disease as part of IBS work-up
3. [3]Canadian Society of Clinical Chemists / Choosing Wisely Canada (2025). Clinical Biochemistry recommendations. linkChoosing Wisely Canada: don't order tTG-IgG or DGP antibody testing for initial celiac screening
4. [4]Ontario Ministry of Health (2026). Ontario Health Insurance Plan: Schedule of Benefits for Laboratory Services (effective April 1, 2026). linkTwo tests (L570 tTG-IgA, L571 serum IgA) are insured for celiac diagnosis under the 2026 Schedule
5. [5]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
6. [6]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
7. [7]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