At a glance
Also known as
Tissue transglutaminase antibodies; tTG IgA; tTG IgG; Anti-tTG; Gliadin antibodies; Endomyseal antibodies; Endomysium Ab; Gluten-sensitive enteropathy tests
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.
A blood sample drawn from a vein in your arm
Test preparation needed?
Follow your doctor's instructions.
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 and to a lesser extent oats (gluten the alcohol soluble part of gliadin from wheat, avenin from oats, secanin from rye and hordein from barley). In the past, the only way to diagnose coeliac disease was by examination of a tissue 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 (anti-tTG), : Tissue transglutaminase is an responsible for crosslinking certain . 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 , 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. European diagnostic guidelines have encouraged the use of EMA, although that is because of the use of poorer standard tTG tests being used than generally used in Australia.
- 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 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 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.
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 look for the markers that are strongly associated with 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 general 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.