Coeliac disease blood test: which values say enough

A coeliac blood test comes down mainly to one antibody: anti-tissue-transglutaminase, Anti-TTG (IgA) for short. In coeliac disease it is almost always raised, with a sensitivity and specificity around 90 to 98% (PMID 35043426). Two other values make the result reliable: Endomysium IgA and Total IgA.

Sounds technical, but the logic is simple. Anti-TTG sieves, Endomysium IgA confirms, and Total IgA checks whether the test can work in you at all. Without that third value you miss the people in whom the test reads falsely normal.

And the most important condition stands apart from any value: you must still be eating gluten when your blood is drawn. What coeliac disease is exactly is in coeliac disease: symptoms, testing and gluten-free living.

Which blood values show coeliac disease?

A coeliac test consists of three blood values that work together. Anti-TTG is the first sieve, Endomysium IgA confirms a positive result, and Total IgA checks whether you make enough IgA. Only together do they give a reliable picture.

With a strongly raised Anti-TTG, for example more than ten times the upper limit, the chance of coeliac disease is very high (PMID 38176661). Your doctor decides whether an additional gut biopsy is needed to complete the diagnosis.

You can have Anti-TTG and Endomysium IgA measured together through the coeliac disease blood test, with Total IgA alongside as a check.

Why must you keep eating gluten before the test?

The test measures the immune reaction to gluten. Eat no gluten, and there is nothing to react to, so the antibodies drop. A coeliac test during a gluten-free diet can therefore read falsely normal, even if you do have coeliac disease.

This is the most common mistake. Someone feels better without bread, only then gets tested, and gets a normal result that rules nothing out. The test has become worthless.

So keep eating gluten until your blood is drawn, usually daily for several weeks to months. If you are unsure how much and how long, discuss it with your GP first.

What if your Total IgA is too low?

Some people naturally make little IgA, a so-called IgA deficiency. In them, the Anti-TTG (IgA) can stay low while coeliac disease is present. That is why Total IgA belongs in the panel as standard: it exposes this trap.

If your Total IgA is too low, your doctor switches to IgG-based tests, such as anti-TTG IgG. That way you still get a usable result. This is exactly why one single antibody is rarely enough.

The difference between coeliac disease, a wheat allergy and gluten sensitivity, and which test fits, is in the gluten intolerance test.

What does a positive result mean?

A positive blood test makes coeliac disease likely, but is not yet an endpoint. In adults the diagnosis is usually confirmed with a gut biopsy, where your doctor checks whether your villi are damaged (PMID 28760445). Only then is the diagnosis certain.

So with an abnormal result, do not go gluten-free yourself before the biopsy is done. That can blur the picture. Let your GP decide the next steps.

A low iron that comes with the result deserves separate attention. Why iron stays so stubbornly low in coeliac disease is in coeliac disease, iron deficiency and unexplained fatigue. Which symptoms in women can point to coeliac disease is in recognising coeliac disease symptoms in women.

How do you get your coeliac values tested?

If you want your coeliac values measured, do it while you are still eating gluten. You can test for coeliac disease with Anti-TTG and Endomysium IgA, or pick individual markers through building your own blood test. Add Total IgA for safety.

Always discuss an abnormal result with your GP. The NHG and Thuisarts look at the whole picture in coeliac disease: your complaints, your blood values and, if needed, a biopsy, not one number.

References

1. Coeliac disease serology: a systematic review with meta-analysis of the accuracy of serological tests to support the diagnosis. Aliment Pharmacol Ther. 2022. PMID 35043426.
2. Accuracy of the No-Biopsy Approach for the Diagnosis of Celiac Disease in Adults: A Systematic Review and Meta-Analysis. Gastroenterology. 2024. PMID 38176661.
3. Lebwohl B, Sanders DS, Green PHR. Coeliac disease. Lancet. 2018;391(10115):70-81. PMID 28760445.
4. Singh P, Arora A, Strand TA, et al. Global Prevalence of Celiac Disease: A Systematic Review and Meta-analysis. Clin Gastroenterol Hepatol. 2018;16(6):823-836. PMID 29551598.
5. NHG and Thuisarts. Information on coeliac disease and blood testing. Available via thuisarts.nl.

Every blood test result at Lunara includes a professional assessment by a BIG-registered doctor. For treatment decisions, discuss your results with your GP.