Summary

• Coeliac disease is a life-long, inherited condition in which your small intestine becomes inflamed when you eat gluten or other similar proteins.
• It occurs because your immune system, which is designed to protect you from harmful things, mistakenly attacks your small intestine when it detects gluten.
• It does this by producing antibodies.
• Testing for coeliac disease typically involves having blood tests to see if you have these antibodies.
• If your results are positive, you may be asked to have a biopsy in which a small section of your intestine is removed and examined. This can give a definite diagnosis.
• Genetic tests for coeliac disease are available but are limited in what they can do.

What is coeliac disease and how is it tested?

Coeliac disease is an inherited autoimmune disorder in which your immune system responds to gluten or other proteins in wheat, rye, barley and oats and mistakenly attacks the lining of your small intestine.

The tiny finger-like projections, called villi, that line the walls of your intestine become inflamed and flattened making it more difficult for your body to absorb nutrients from food.

Your immune system protects you by making antibodies to fight off harmful things like bacteria and viruses and then help your body eliminate them. In autoimmune conditions like coeliac disease, it produces antibodies that wrongly attack your own cells.

If you have coeliac disease, your immune system makes antibodies when it detects gluten and other proteins. The antibodies cause inflammation that damages the lining of the small intestine.

Typically, two blood tests are used to check for the antibodies that are produced by the immune system in coeliac disease. If the antibody tests are positive, or if you have severe symptoms, a biopsy of your small intestine is needed to confirm the diagnosis.

Coeliac disease can occur at any age but is most often diagnosed at two different age ranges. These are either in babies aged between 8 and 12 months old, or in people aged between 40 to 60 years.

The gene changes that make you more likely to have coeliac disease.

Almost everyone with coeliac disease has inherited genes that have changes in them that give them a greater chance of having the disease. These are HLA-DQ2 and HLA-DQ8. However, while it is thought that more than half of people in Australia carry one or both genetic changes, called variants, only a small percentage of people go on to have symptoms. This means testing for genetic variants cannot give a definitive diagnosis of coeliac disease.

Coeliac disease cannot be fully explained by these genetic variants alone. It is thought that many factors contribute. These include genetics, the environment, and the immune system. 

Why get tested?

Your doctor may order tests for coeliac disease, if:

• you have gut symptoms such as pain, bloating, flatulence, nausea, vomiting, diarrhoea and/or constipation, or;
• you’ve had blood test results that suggest you are not properly absorbing nutrients such as iron, vitamin B12, folate, vitamin D and calcium.

Although coeliac disease is fairly common, most people who have it are not aware of it. This is partly because even when there is intestinal damage there may be no symptoms or else they are mild and non-specific. Since these symptoms may also be due to a variety of other conditions, a diagnosis of coeliac disease may be missed or delayed, sometimes for years.

Sometimes testing will be ordered to screen for coeliac disease when you do not have symptoms but have close relatives with coeliac disease, especially if you have another autoimmune disorder such as type 1 diabetes, autoimmune thyroid disease or others. The later the age of diagnosis, the greater the chance of developing another autoimmune disorder.

Blood tests

Typically, two blood tests are used to check for coeliac antibodies. 

In both tests, the laboratory measures two types of the immunoglobulins that make up each of the antibodies. These are IgA (immunoglobulin A) and IgG (immunoglobulin G).

IgA is the most useful form of the test because IgA antibodies are made in the intestine. However, some people are naturally deficient in IgA. If you are deficient in IgA and have coeliac disease you will receive a falsely negative result if only IgA is measured.

This why the IgG test is often requested together with an IgA test.

Biopsy testing

Antibody tests are very successful at detecting coeliac disease, but a definite diagnosis needs a biopsy of your small intestine.

Genetic testing

About 99 per cent of people with coeliac disease have variants on one or both of two genes, HLA-DQ2 and HLA-DQ8. Genetic testing is available, but a positive result cannot diagnose coeliac disease since many people carry the genetic variants but do not have the disease.

Genetic testing is useful for family members of people with coeliac disease that fall into a high-risk category and for people with blood test results that are inconclusive.

Tests for related conditions

Other tests to help assess the severity of the disease and to check for malnutrition and malabsorption problems can include some of these tests:

• FBC (full blood count) to see if you have anaemia.
• CRP (C-reactive protein) to look for inflammation.
• ESR (erythrocyte sedimentation rate) to look for inflammation.
• Electrolytes and LFTs (Liver Function Tests) to measure electrolyte, protein and calcium levels, and to assess your kidney and liver function.
• Iron studies.
• Vitamins D, E, and B12 and folate to measure vitamin deficiencies.
• Allergy testing, especially lactose intolerance since people with coeliac disease often have other food intolerances.

Having the test

Sample

Blood.

Any preparation?

When you are being tested for antibodies or having a biopsy, it is important that you continue to eat gluten in your diet. If you are on a gluten-free diet your doctor will ask you to eat two slices of wheat-bread per day for at least two weeks beforehand.

Your results

If you are on a normal diet and eating food that contains gluten, tests results that show high levels of Transglutaminase IgA antibody and anti-gliadin IgA antibodies suggest you may have coeliac disease. You may be asked to have a biopsy. A biopsy is the only way to make a certain diagnosis of coeliac disease.

If you are one of those people who has an IgA-deficiency these tests will be falsely low and IgG-based tests will be used.

Genetic testing for HLA-DQ2 and HLA-DQ8 variants will generally be used to exclude coeliac disease.

Treatment and monitoring

Everyone diagnosed with coeliac disease must follow a gluten-free diet. This allows your intestines to heal.

Antibody tests are used to monitor your progress. Antibody levels should fall when gluten is removed from your diet, but it may be many months before you see a negative result – a result that detects no antibodies.

If antibody levels do not fall and your symptoms are not improving, there may be hidden forms of gluten in your diet. Gluten is often found in unexpected places, from salad dressings to cough syrup. Otherwise, you may have one of the rare forms of coeliac disease that does not respond to dietary changes. New treatments are being developed for these rare conditions and your doctor will advise on the best way forward.

Even if you have coeliac disease but no symptoms, it is still recommended that you follow a gluten-free diet. You will have inflamed villi in your intestines, and you may have malabsorption problems that are causing silent conditions such as osteoporosis (weak bones).

More to know?

It is possible to have an allergy to grains such as wheat and rye, in which case your immune system will make specific IgE (Immunoglobulin E) antibodies. These antibodies may cause symptoms that are similar to those of coeliac disease but will only last for a short time after you eat the food to which you are allergic. The reaction may be mild or severe, but it is limited and does not cause damage to the lining of your intestine the way that coeliac disease does. Your doctor can order tests for these specific IgE antibodies.

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask: 

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

More information

Pathology and diagnostic imaging reports will be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

Look for a link to Pathology Tests Explained in your Pathology Results Report page and in the my health app.

Get further trustworthy health information and advice from healthdirect.