Coeliac Serology Interpreter
Coeliac Serology Interpreter
Interpret anti-tTG IgA, total IgA and EMA together, and see why a gluten-free diet before testing invalidates the result.
Coeliac Serology
tTG + IgA + EMA → interpretationAnti-tTG IgA 12× ULN, IgA normal, EMA not done
Decision logic
Anti-tTG IgA ≥ 10× ULN + positive EMA → no-biopsy pathway may apply
Anti-tTG IgA ≥ 10× ULN → strongly positive, confirm with EMA
Anti-tTG IgA 1 – 10× ULN → positive, refer for biopsy
Anti-tTG IgA < 1× ULN → negative
- gluten challenge
- the patient must be eating gluten for at least six weeks before testing — a negative result on a gluten-free diet is uninterpretable
- no-biopsy pathway
- anti-tTG ≥ 10× ULN with a positive EMA on a separate sample; established in children, increasingly accepted in adults, but a specialist decision
- total IgA
- must always be checked alongside — deficiency makes IgA-based tests falsely negative
Worked example
Anti-tTG IgA 12× ULN, IgA normal, EMA not done
IgA is normal → the IgA-based tTG result is valid
Anti-tTG 12× ULN meets the 10× threshold, and EMA is not done → strongly positive
Confirm with EMA on a separate sample before considering the no-biopsy pathway
Interpreting the pattern
| Anti-tTG IgA | EMA | IgA status | Interpretation |
|---|---|---|---|
| ≥ 10× ULN | Positive | Normal | Coeliac disease likely — no-biopsy pathway may apply |
| ≥ 10× ULN | Not done or negative | Normal | Strongly positive — confirm with EMA |
| 1 – 10× ULN | Any | Normal | Positive — refer for biopsy |
| < 1× ULN | Any | Normal | Negative — coeliac disease unlikely |
| Any | Any | Deficient | Uninterpretable by IgA-based tests — request IgG-based serology |
The two pitfalls that make serology unreliable
The single most important condition on this test is that the patient must be eating gluten for at least six weeks beforehand. Coeliac serology reflects an active immune response to dietary gluten, and a patient who has already started a gluten-free diet — often on their own initiative, after reading about the condition — can produce a falsely negative or falsely low result that is simply uninterpretable rather than reassuring.
The second pitfall is IgA deficiency, which is roughly ten times commoner in people with coeliac disease than in the general population and makes any IgA-based test, including anti-tTG IgA, falsely negative. Total IgA should be checked alongside every request; when it is deficient, IgG-based tests — IgG-tTG or IgG-DGP — are needed instead.
The no-biopsy pathway, in which a sufficiently high anti-tTG result combined with a positive EMA on a separate sample allows a diagnosis without duodenal biopsy, is well established in children and increasingly accepted in adults, but applying it remains a specialist decision that weighs the whole clinical picture. Anti-tTG can also be weakly positive in conditions unrelated to coeliac disease, including type 1 diabetes, autoimmune liver disease, heart failure and some infections, which is why a weak positive result is treated differently from a strong one.
Frequently asked questions
Do I need to be eating gluten before coeliac testing?
Yes — for at least six weeks beforehand. A negative result in someone already on a gluten-free diet is uninterpretable, not reassuring, because the antibody response depends on ongoing gluten exposure.
What does the no-biopsy pathway mean?
Anti-tTG IgA at ten times the upper limit of normal or more, confirmed by a positive EMA on a separate sample, can support a diagnosis of coeliac disease without duodenal biopsy. It is established in children and increasingly used in adults, but remains a specialist decision.
Why check total IgA alongside anti-tTG?
IgA deficiency is about ten times commoner in coeliac disease and makes IgA-based serology, including anti-tTG IgA, falsely negative. If IgA is deficient, request IgG-tTG or IgG-DGP instead.
Can anti-tTG be positive without coeliac disease?
Yes, weakly. Type 1 diabetes, autoimmune liver disease, heart failure and some infections can all produce a weak positive. This is one reason a weak positive is referred for biopsy rather than treated as diagnostic on its own.
Related calculators
References
- Husby S et al. European Society for Paediatric Gastroenterology, Hepatology and Nutrition Guidelines for Diagnosing Coeliac Disease 2020. J Pediatr Gastroenterol Nutr. 2020;70(1):141–56.
- Al-Toma A et al. European Society for the Study of Coeliac Disease (ESsCD) guideline for coeliac disease and other gluten-related disorders. United European Gastroenterol J. 2019;7(5):583–613.