What is coeliac disease?

Coeliac disease is a chronic illness that develops in genetically susceptible people when the immune system reacts abnormally to a protein called gluten.

Gluten is found chiefly in wheat, barley and rye.

When a person with coeliac disease eats gluten, the immune system mounts a reaction against the inner surface of the small bowel. As a result the small finger-like structures called villi, which carry out the absorption of food, may be damaged.

The disease affects not only the bowels; it can also affect the blood count, bone health, the nervous system and other organs.

Coeliac disease is not a food allergy, and it is not contagious.

How does gluten damage the bowel?

The normal surface of the small bowel carries millions of tiny villi. These increase the surface area of the bowel and so allow iron, vitamins, minerals, fats and other nutrients to be absorbed.

In coeliac disease, contact with gluten activates the immune system.

Put simply, the process is this:

Gluten is eaten → the immune system is activated → inflammation in the small bowel → damage and flattening of the villi → disturbance of the absorption of food

But not every patient develops the same degree of bowel damage or malabsorption.

In whom does it occur?

Coeliac disease can appear in children and in adults alike.

Genetic susceptibility matters. The great majority of patients carry one of the genetic features called HLA-DQ2 or HLA-DQ8.

But carrying these genes does not by itself mean coeliac disease. A great many people in the population carry them and never develop the illness.

People who have coeliac disease in a first-degree relative are at higher risk than the rest of the population.

Coeliac disease may also be seen more often alongside certain autoimmune diseases, such as type 1 diabetes and autoimmune thyroid disease.

What are the symptoms?

Coeliac disease can present in very different ways.

Some patients have the typical digestive complaints; in others there may be no diarrhoea at all.

The digestive symptoms may include:

Diarrhoea,
Abdominal bloating,
Wind,
Abdominal pain,
Weight loss,
Nausea,
Indigestion.

But coeliac disease does not present with bowel symptoms alone.

Symptoms outside the bowel

In some patients the first finding may be:

Iron deficiency anaemia,
Weakness and tiredness,
Folate or B12 deficiency,
A fall in bone mineral density,
Vitamin D deficiency,
Recurrent mouth ulcers,
Unexplained raised liver tests,
Certain neurological symptoms.

In children, failure to grow and develop may be seen.

For this reason the thought “I have no diarrhoea, so I cannot have coeliac disease” is not correct.

What is dermatitis herpetiformis?

It is one of the important findings of coeliac disease outside the bowel.

It is a skin condition seen particularly around the elbows, knees, buttocks and scalp, which is intensely itchy and runs with small blisters.

It is closely associated with coeliac disease, and assessing it may need dermatology and gastroenterology to work together.

How is coeliac disease diagnosed?

One of the most important points in making the diagnosis is this:

A gluten-free diet should not be started before the investigation for coeliac disease is complete.

This is because stopping gluten may return the blood tests and the bowel biopsy to normal, and that can make an accurate diagnosis difficult.

The 2025 ESsCD guideline likewise recommends specifically that coeliac serology be done while a gluten-containing diet is continuing.

Blood tests

One of the tests of first choice in adults is:

IgA anti-tissue transglutaminase (anti-TG2/tTG-IgA).

Measuring total IgA at the same time is also important, because in people with IgA deficiency the standard IgA tests can be misleadingly negative.

The 2025 European guideline recommends IgA anti-TG2 with a simultaneous total IgA as the initial test.

Gastroscopy and duodenal biopsy

One of the classical and important methods of diagnosis in adults is taking biopsies from the duodenum during a gastroscopy.

Under the microscope, the structure of the villi, the inflammation and the other changes consistent with coeliac disease are assessed.

Because the damage in coeliac disease may not be the same everywhere in the bowel, a biopsy from a single point may not be enough.

For the standard biopsy approach in adults, the 2025 European guideline recommends at least four biopsies from the second part of the duodenum, and a further two from the duodenal bulb.

Can coeliac disease now be diagnosed without a biopsy?

There is an important update on this.

In some selected adults, yes.

The 2025 ESsCD guideline conditionally recommends an approach that allows the diagnosis to be made without a biopsy in selected adults under 45 whose IgA anti-TG2 level is ten times the upper limit of normal or above, when certain conditions are met.

The result must be confirmed on a second, independent blood sample, and the patient must go on eating gluten throughout. The decision is recommended to be made with specialist assessment.

So:

There is no general rule that “my coeliac test was positive, so an endoscopy is no longer needed”.

The decision must be made according to the individual patient.

Is genetic testing needed?

HLA-DQ2 and HLA-DQ8 tests are not done routinely in everyone.

The real value of these tests is that they help to exclude coeliac disease.

Finding HLA-DQ2/DQ8 does not prove the diagnosis, because a substantial proportion of healthy people also carry these genetic features.

The absence of both, on the other hand, makes coeliac disease very unlikely.

They can be particularly useful in people whose diagnosis is uncertain, or in patients who have already started a gluten-free diet.

The treatment of coeliac disease

The mainstay of treatment for coeliac disease is a lifelong gluten-free diet.

The 2025 ESsCD management guideline likewise treats a strict, lifelong gluten-free diet as the cornerstone of treatment.

Foods containing wheat, barley and rye must be avoided.

But eating gluten-free is not simply a matter of giving up bread and pasta. Gluten can be present in processed foods, in sauces, and in products where it is not expected.

For this reason the support of a dietitian experienced in coeliac disease is very helpful, particularly in the period after diagnosis.

Can oats be eaten?

This is one of the questions patients ask most often.

Pure oats, uncontaminated by gluten, can be tolerated by most people with coeliac disease.

But ordinary commercial oat products may be contaminated with wheat, barley or rye during production or packaging.

It is therefore important that the product used has been reliably produced as gluten-free.

Since some people with coeliac disease may also be sensitive to oats, an individual assessment is needed.

Can a very small amount of gluten do harm?

The approach of “a little gluten will not matter” is not correct in coeliac disease.

Damage may occur in the bowel even when the person feels no marked complaint after eating gluten.

For this reason the aim of treatment is not only to abolish the diarrhoea or the bloating, but to allow the bowel lining to heal and to reduce the risk of long-term complications.

The current European guideline recommends keeping daily gluten exposure as low as possible, and maintaining a strict gluten-free diet.

Does cross-contamination matter?

Yes.

If a gluten-free food comes into contact with gluten-containing foods while it is being prepared, it may become unsuitable for a person with coeliac disease.

For instance, using the same:

Toaster,
Chopping board,
Floured surfaces,
Frying oil

can cause cross-contamination.

But an excessive fear that makes the patient’s life needlessly difficult should also be avoided. The aim is a well-informed and sustainable gluten-free life.

Is there a drug treatment?

At present there is no approved drug treatment that takes the place of the gluten-free diet in standard coeliac disease.

Where there are deficiencies of vitamins, iron, folate or other nutrients, these are treated separately.

New drugs for coeliac disease are being investigated; but in day-to-day clinical practice the mainstay of treatment remains the gluten-free diet.

Is follow-up needed?

Yes.

It is not right for a patient to be told “eat gluten-free” once the diagnosis is made and then left without follow-up.

Follow-up assesses:

Whether the complaints have settled,
Adherence to the gluten-free diet,
The course of the coeliac antibodies,
Anaemia and deficiencies of vitamins and minerals,
Bone health where needed.

Other checks may be needed according to the patient’s age and risks. The current European guideline stresses in particular the importance of structured long-term follow-up.

What if the complaints do not settle despite the diet?

This does not always mean that the coeliac disease is not responding to treatment.

The first things assessed are whether the diagnosis is correct, and whether gluten is being eaten unknowingly.

Beyond that, lactose intolerance, irritable bowel syndrome, microscopic colitis, pancreatic disease or other conditions may cause similar complaints.

So where complaints continue, the cause should be investigated rather than the diet simply being restricted further.

What is refractory coeliac disease?

In a very small number of patients, the damage in the small bowel may continue despite a strict gluten-free diet.

Once other causes have been excluded, this may be assessed as refractory coeliac disease.

It is a rare condition and different from ordinary coeliac disease; it needs detailed assessment and specific treatment in experienced centres.

Does coeliac disease lead to cancer?

The great majority of people with coeliac disease do not develop cancer.

But the risk of certain rare lymphomas and of small bowel tumours may be increased, particularly where the disease has gone undiagnosed for a long time or is not controlled.

So while it is not right to make more of the cancer risk than it deserves, neither is it right to see coeliac disease as a simple food intolerance, a matter of “gluten disagrees with me”.

Accurate diagnosis, adherence to the gluten-free diet and regular follow-up matter for long-term health.

Are coeliac disease and gluten sensitivity the same thing?

No.

Coeliac disease, wheat allergy, and non-coeliac wheat/gluten sensitivity are different conditions.

In coeliac disease there is a specific immune mechanism, and in suitable patients bowel damage can be demonstrated.

For this reason a person cutting gluten out on their own, saying “gluten disagrees with me”, does not amount to a diagnosis of coeliac disease.

Where coeliac disease is a possibility in particular, it is very important that the tests are done before a gluten-free diet is started.

What is the outlook?

The outlook in coeliac disease with appropriate treatment is generally very good.

When gluten is removed completely, the complaints lessen in the great majority of patients, the coeliac antibodies fall over time, and the lining of the small bowel begins to heal.

In adults, complete healing of the bowel lining may take longer than the settling of the symptoms.

Although coeliac disease is a chronic illness, with the right diet and regular follow-up the great majority of patients can lead a normal and active life.

Currency: The 2025 European Society for the Study of Coeliac Disease (ESsCD) guideline on the diagnosis of adult coeliac disease, together with its recommendations on management and follow-up, was taken into account in preparing this information.

This content is for general information. People in whom coeliac disease is suspected are advised not to start a gluten-free diet on their own before their diagnostic investigations are complete.