Coeliac disease tests
At a Glance
Why Get Tested?
To help determine whether you have coeliac disease and to evaluate the effectiveness of a gluten-free diet
When to Get Tested?
When you have symptoms suggesting coeliac disease, such as chronic diarrhoea, abdominal pain, anaemia and weight loss, unexplained liver abnormalities or osteoporosis; when an infant is chronically irritable or fails to grow at a normal rate; when a family member has coeliac disease; to monitor treatment of coeliac disease.
In those with Type 1 diabetes, Down or Turner syndromes, there is around a 5-10% life time risk of developing coeliac disease. These patients are often screened annually or genetic testing may be performed.
Sample Required?
A blood sample drawn from a vein in your arm
Test Preparation Needed?
Follow your doctor's instructions.
The Test Sample
What is being tested?
Coeliac disease tests are a group of assays developed to help diagnose coeliac disease and a few other gluten-sensitive conditions. These tests detect autoantibodies that the body produces as part of an inappropriate immune response to dietary proteins found in wheat, rye and barley (gluten and gliadin). In the past, the only way to diagnose coeliac disease was by examination of a tissue biopsy of the small intestine. While this microscopic evaluation 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 (TTG), IgA: Tissue transglutaminase is an enzyme responsible for crosslinking certain proteins. 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 IgG anti-TTG, 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 the previous generation gliadin tests is no longer considered acceptable in any aspect of coeliac disease.
Two other blood tests that are now rarely used:
- Anti-endomysial antibodies (EMA), IgA: Endomysium is the thin connective tissue layer that covers individual muscle fibres. Anti-endomysial antibodies are developed in reaction to the ongoing damage to the intestinal lining. It has been found that tissue transglutaminase (TTG) is the substance detected in this test. 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. The test is more difficult to do and interpret properly than anti-TTG.
- Anti-reticulin antibodies (ARA), IgA: Anti-ARA is not as specific or sensitive as the other autoantibodies. 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 specific for coeliac disease (since IgA is the type of antibody made in the intestine) and is measured almost exclusively. 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 the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
Follow your doctor's instructions. For diagnosis, ingestion of gluten-containing foods for a time period, such as several weeks, is necessary. For monitoring, no preparation is necessary.
The Test
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).
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 test result mean?
| Anti-TTG antibodies, IgA | Total IgA | Anti-TTG antibodies, IgG | Anti-gliadin antibodies (AGA), IgG | Diagnosis |
|---|---|---|---|---|
| + | + | Presumptive coeliac disease | ||
| – | + | – | – | Symptoms not likely due to coeliac disease |
| – | – | + | + | Possible coeliac disease, false negative anti-TTG, IgA due to total IgA deficiency |
Positive and indeterminate coeliac disease tests are usually followed by an intestinal biopsy. A biopsy is used to make a definitive 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
Ask a Laboratory Scientist
Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
