Gluten intolerance test: coeliac disease, allergy or sensitivity?

If you take one thing from this article, let it be this: keep eating gluten until your blood has been drawn. If you have already been gluten-free for a month, your antibodies drop. The test then reads negative, even when you do have coeliac disease.

I find that the cruellest trap in the whole diagnostic path. You do the thing that feels logical. You skip the bread, you feel better, and that is exactly why you never get a diagnosis. For coeliac disease you have to eat the thing that makes you ill, just to prove that it does.

What is the difference between coeliac disease, wheat allergy and gluten sensitivity?

These three get mixed up daily, while biologically they have nothing to do with each other. Coeliac disease is an autoimmune condition. Wheat allergy is an allergy. Gluten sensitivity is a leftover category where neither can be demonstrated. Only the first two can be brought into view with blood testing.

That distinction is not academic. In coeliac disease gluten damages your small intestine even when you barely notice it, and that can lead to anaemia and bone loss. In gluten sensitivity there is no demonstrable damage and you can decide for yourself what you tolerate.

How common is coeliac disease, and is it more common in women?

In a global meta-analysis, prevalence sat at 1.4 percent on blood testing, and at 0.7 percent counting only biopsy-confirmed cases. Women came out more often than men: 0.6 versus 0.4 percent (PMID 29551598).

That fits the wider picture. Of everyone with an autoimmune disease, 78 percent are women (PMID 18688037), and coeliac disease belongs in that category. More on that under autoimmune disease symptoms in women.

Coeliac disease can appear at any age, including after a lifetime of eating bread without complaint. The idea that it is "a childhood thing" is wrong.

Which blood values belong to a gluten intolerance test?

For coeliac disease it comes down to two antibodies. Anti-TTG IgA is the first choice, and endomysial IgA is used to confirm a positive result because it is almost never falsely positive. A total IgA belongs with them as standard, and that third one is the one everybody forgets.

Why that total IgA counts: roughly one in five hundred people makes too little IgA. In them, every IgA-based test is automatically negative, even when they have coeliac disease. Without that total IgA you do not know whether you are reading a real result or an empty one (PMID 26796833).

Imagine two women of 41, both having anti-TTG drawn, both getting a negative result. One was still eating bread, and for her negative really means negative. The other had been gluten-free for three months, and for her that result says nothing at all.

Why must you keep eating gluten before the test?

The test measures antibodies your body makes in response to gluten. Remove the gluten and the trigger disappears, so the antibodies fall, often within weeks. The damage heals, the antibodies drop, and the test turns negative. That is precisely why a gluten-free diet should not be started before the diagnosis is settled (PMID 26796833).

If you have already stopped and still want testing, you will need to reintroduce gluten before drawing blood is worthwhile. Discuss that with your GP, because the duration and the amount matter. The Maag Lever Darm Stichting and Thuisarts provide information on this.

Do not do this alone if it makes you very ill. Then the conversation with your GP matters more than the result.

Which symptoms fit coeliac disease?

The classic picture is diarrhoea and weight loss, but in adult women it often looks quite different. Many people with coeliac disease have barely any gut complaints and turn up with something that seems unrelated.

• Iron deficiency or anaemia that does not respond to supplements.
• Fatigue out of proportion to your life.
• Abdominal pain, bloating or changing stools.
• Bone loss at an age where it is not expected.
• Unexplained infertility or repeated miscarriage.

The first is the clue I see missed most often. Iron is absorbed in exactly the stretch of gut that coeliac disease damages. So a deficiency that refuses to recover deserves a second look. What a low iron means sits under the ferritin value.

What can you test?

At Lunara you can take the coeliac panel, with anti-TTG and endomysial IgA. Keep eating gluten in the weeks before you draw blood, or you are buying a result that is worthless.

A positive blood result is not an endpoint either. In adults, coeliac disease is usually confirmed with a small-bowel biopsy via your GP and a gastroenterologist. So treat blood testing as the first step, not the last.

To look more broadly at whether inflammation is measurable at all, you can pick CRP and ESR through building your own blood test. How to read those two sits in the overview on what CRP and ESR mean.

References

1. Rashid M, Lee J. Serologic testing in celiac disease: practical guide for clinicians. Can Fam Physician. 2016;62(1):38-43. PMID 26796833.
2. Singh P, Arora A, Strand TA, et al. Global prevalence of celiac disease: systematic review and meta-analysis. Clin Gastroenterol Hepatol. 2018;16(6):823-836. PMID 29551598.
3. Fairweather D, Frisancho-Kiss S, Rose NR. Sex differences in autoimmune disease from a pathological perspective. Am J Pathol. 2008;173(3):600-609. PMID 18688037.
4. Maag Lever Darm Stichting, NHG and Thuisarts. Information on coeliac disease and gluten-free eating. Available via mlds.nl and 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.