What is being tested?Coeliac antibody tests help in the diagnosis of
coeliac disease, and also can help to rule out this diagnosis. These tests detect autoantibodies that the body creates as part of an immune response to dietary proteins (gluten and gliadin) found in wheat, rye, and barley. These autoantibodies are involved in inflammation in the gut and damage to the lining of the gut wall. This damage results in symptoms associated with
malnutrition and malabsorption, such as
abdominal pain
abdominal bloating/distention
chronic diarrhoea
weight loss
oral ulceration
weakness
fatigue
anaemia
bleeding tendency
bone and joint pain
irritability and delayed growth and development in infants & children
Patients with celiac disease will not typically have all these symptoms, but may have a selection from this list. None of these symptoms are diagnostic of coeliac disease, as they can be found in other (gut) conditions.
In the past the only way to diagnose coeliac disease was to study a biopsy of the small intestine under the microscope. While this microscopic evaluation remains the very best test and is often still used to confirm a diagnosis of coeliac disease, the availability of less invasive blood tests used to screen for coeliac disease have reduced the number of biopsies needed. Autoantibody blood tests that are currently widely available include:
- Anti-tissue Transglutaminase Antibody (TTG), IgA: Tissue transglutaminase is an enzyme responsible for crosslinking certain proteins, and is found in the gut as well as in other tissues. It has been identified as the target molecule for the anti-endomysial antibodies described earlier. Although “tissue” is in the name of this autoantibody, it nevertheless involves testing blood and not tissue. Over 90% of patients with untreated coeliac disease have anti-TTG, IgA antibodies.
- Anti-Endomysial Antibodies (EMA), IgA: Endomysium is the thin connective tissue layer that covers individual muscle fibres. Anti-endomysial antibodies are developed as part of the ongoing damage to the intestinal lining. Over 90% of patients with active coeliac disease Anti-EMA, IgA antibodies have very high specificity (few false positives), of almost 100%.
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70% of patients with dermatitis herpetiformis (another gluten-sensitive disease that causes an itchy burning blistering rash on the skin) will have anti-EMA or anti-TTG, IgA antibodies.
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There are 5 types of antibody IgG, IgA, IgM, IgD, IgE in the body. While both IgG and IgA types of each autoantibody will often be present in the blood they are not equally specific for coeliac disease. In general, the IgA forms of the tests tend to be more specific for the diagnosis of coeliac disease, and in many laboratories IgA antibodies alone are tested.
IgG versions of the autoantibodies may be requested to either complement the IgA antibody testing and/or used because someone has an overall deficiency in IgA. This happens about 2-3% of the time with coeliac disease and can lead to some false negative test results.
- Anti-gliadin and anti-reticulin antibodies are two other well known autoantibodies that used to be widely tested in the evaluation of suspected celiac disease. However they both have lower sensitivity (more false negatives) and lower specificity (more false positives) than anti-EMA and anti-TTG antibodies. These two antibodies are therefore not widely tested for in the UK. Antigliadin antibodies may still have a role in the testing of children, particularly in infants under the age of 2 years.
