What is being tested?

Coeliac disease tests have been developed to help diagnose coeliac disease and a few other gluten-sensitive conditions. These tests detect autoantibodies that the body produces to dietary proteins found in wheat, rye and barley and to a lesser extent oats. In the past, the only way to diagnose coeliac disease was by examination of a biopsy of the small intestine. While this biopsy is still considered the gold standard and is still used to confirm a diagnosis of coeliac disease, the availability of less invasive blood tests to screen for coeliac disease has reduced the number of biopsies needed.

Autoantibody blood tests that are available include:

• Anti-tissue transglutaminase antibody (anti-tTG), IgA: Although ‘tissue’ is in the name of this autoantibody, it nevertheless involves testing blood and not tissue since the autoantibody is found in the blood. A few laboratories also offer tests to detect anti-tTG IgG, though these are best used in patients who are IgA deficient.
• Anti-modified or deamidated gliadin antibodies (AGA), IgG and IgA: Gliadin is part of the gluten protein found in wheat (similar proteins are found in rye, barley and oats). AGA is an autoantibody against the gliadin portion.
  The use of older tests is no longer considered appropriate.

Two other blood tests that are now rarely used:

• Anti-endomysial antibodies (EMA), IgA: Anti-endomysial antibodies are developed in reaction to the ongoing damage to the intestinal lining. Almost 100% of patients with active coeliac disease and 70% of patients with dermatitis herpetiformis (another gluten-sensitive condition that causes an itchy, burning, blistering rash on the skin) will have anti-EMA, IgA antibodies. 
• Anti-reticulin antibodies (ARA), IgA: Anti-ARA testing is not as useful as the other tests. It is found in about 60% of coeliac disease patients and about 25% of patients with dermatitis herpetiformis.

Each of the coeliac blood tests measures the amount of a particular autoantibody in the blood. For each test, both IgG (immunoglobulin G) and IgA (immunoglobulin A) antibodies can be measured; however, few laboratories offer IgG tests other than for gliadin. IgG and IgA are two of the five classes of antibody proteins that the immune system creates in response to a perceived threat.

In general, the IgA antibody is more useful for coeliac disease testing (since IgA is the type of antibody made in the intestine). IgG versions may be ordered either to complement the IgA testing and/or ordered because someone has an overall deficiency in IgA. This happens about 2% of the time with coeliac disease and can lead to some false negative test results.

How is it used?

Coeliac disease tests are primarily used to help diagnose coeliac disease. They are usually ordered on patients with symptoms suggesting coeliac disease, including anaemia and abdominal pain.

Sometimes coeliac testing is ordered to screen for asymptomatic coeliac disease in people who have close relatives with coeliac disease (about 10% of these patients have or will develop coeliac disease) and/or in those who have other autoimmune diseases.

Other tests to help determine the severity of the disease and the extent of a patient’s malnutrition, malabsorption, and the involvement of other organs might include:

• FBC (full blood count) to look for anaemia
• ESR (erythrocyte sedimentation rate) to evaluate inflammation
• CRP (C-reactive protein) to evaluate inflammation
• E/LFTs to determine electrolyte, protein and calcium levels, and to verify the status of the kidney and liver
• Vitamins D, E, and B12 and folate to measure vitamin deficiencies
• Stool fat, to help evaluate malabsorption

Since those with coeliac disease may also experience conditions such as lactose intolerance, coeliac tests may be done in conjunction with other intolerance and allergy testing. Anti-tTG and AGA tests may be ordered at intervals on patients who have been diagnosed with coeliac disease to monitor compliance with a gluten-free diet and to help evaluate the effectiveness of treatment; antibody levels should fall when gluten is removed from the diet.

When is it requested?

Coeliac disease tests are ordered when someone has symptoms suggesting coeliac disease, malnutrition, and/or malabsorption - such as diarrhoea, abdominal pain, weakness, fatigue, weight loss and joint pain. They may be ordered as part of an investigation of anaemia or osteoporosis. In children, coeliac disease tests may be ordered when a child exhibits gastrointestinal symptoms, delayed development, short stature and/or a failure to thrive.

Autoantibody levels should initially be ordered when a patient still has gluten in their diet. Positive or indeterminate results will then be confirmed with a biopsy. One or more antibody tests may be ordered when a patient with coeliac disease has been on a gluten-free diet for a period of time. This is done to verify that antibody levels have decreased and to verify that the diet has been effective in relieving symptoms and reversing the intestinal lining damage (this is sometimes still confirmed with a second biopsy).

In children, the use of the ESPGHAN guidelines 2020 is common in Australia. If a |TTG result if is greater than 10 times upper limit of normal and an endomyseal antibody is positive, a biopsy may be avoided. These guidelines do not apply to adults. These guidelines also comment on the use of TTG as the most useful test in screening, something which is standard in Australia.

When a patient’s symptoms have not subsided, coeliac disease tests may be ordered to check for dietary compliance and to help the doctor and patient look for either hidden gluten in the patient’s diet or for other reasons for their unrelieved symptoms. Asymptomatic people may be tested if they have a close relative with coeliac disease, but coeliac disease testing is not recommended, at this time, as a screen for the general population.

What does the result mean?

Positive and indeterminate coeliac disease tests are usually followed by an intestinal biopsy. A biopsy is used to make a certain diagnosis of coeliac disease.

If a patient has been diagnosed with coeliac disease and eliminates gluten from his/her diet, then the autoantibody levels should fall. If they do not fall and the symptoms do not diminish, then there may either be hidden forms of gluten in the diet that have not been eliminated (gluten is often found in unexpected places, from salad dressings to cough syrup to the adhesive used on envelopes) or the patient may have one of the rare forms of coeliac disease that does not respond to dietary changes. When coeliac disease tests are used to monitor progress, rising levels of autoantibodies indicate some form of noncompliance with a gluten-free diet.

If the person being tested has not consumed any gluten for several weeks prior to testing, then coeliac disease tests may be negative (although this may require many months on a gluten-free diet). If the doctor still suspects coeliac disease, they may do a gluten challenge – have the patient introduce gluten into their diet for several weeks or months to see if the symptoms return. At that time, coeliac tests may be repeated or a biopsy may be done to check for villous atrophy (damage to the villi in the intestine).

Is there anything else I should know?

Although coeliac disease is relatively common, about 0.5% of Australians may be affected, most people who have the disease are not aware of it. This is partly due to the fact that the symptoms are variable - they may be mild or even absent, even when intestinal damage is present on biopsied tissue. 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.

Common questions

• What is the difference between coeliac disease and an allergy to wheat and other grains?

Allergies involve hypersensitivity reactions and the creation of specific IgE (Immunoglobulin E) antibodies to grains such as wheat and rye. These antibodies may cause some symptoms similar to those caused by coeliac disease, but they will only do so 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. If you feel that you may have a wheat or other grain allergy talk to your doctor. They can test you for these specific IgE antibodies.

• Can you outgrow or de-sensitise yourself to coeliac disease?

No. Coeliac disease does not go away. Once you have been diagnosed with coeliac disease, you will need to follow a gluten-free diet for life. If you start eating gluten again, you will again damage the lining of your intestines; it just may take a while for the symptoms to come back.

• Do I need to follow a gluten-free diet if I have been diagnosed with coeliac disease but have never had any symptoms?

If you do have asymptomatic coeliac disease, it is recommended that you follow a gluten-free diet. You will still have damaged villi in your intestines and you may have malabsorption problems that are causing silent conditions such as osteoporosis. If you have doubts about the accuracy of your diagnosis, you may want to work with your doctor to verify the findings.

• Can I have oats in my diet?

This is somewhat controversial. More recent evidence suggests that many patients can tolerate oats, though this must be discussed with your doctor and a nutritionist.

• How do I know what to eat and where can I get help?

Your doctor will have some information for you on coeliac disease. You can also visit the links listed under the 'Related information' tab for more information and for organisations that lead to support groups. Since this is a fairly common (if underdiagnosed) disease found throughout the world, there is help available.

• Are there other ways to test for coeliac disease?

Genetic tests that help diagnose coeliac disease have recently become available. These tests look for the human leukocyte antigen (HLA) markers DQ2 and DQ8. A positive result does not diagnose coeliac disease since about 20 - 30% of the healthy population also carry these markers but do not have the disease. A positive result requires confirmation. However, a negative result largely rules out coeliac disease. These tests are most useful for family members of individuals with the disease that fall into a high-risk category and for those with other diagnostic test results that are inconclusive. They are also of use in those with Turner or Down syndromes, as well as Type 1 diabetes.

More information

RCPA Manual: Endomysial antibody

Healthdirect Australia: Coeliac disease and gluten intolerance