Diagnosis

As coeliac disease has significant health implications, a definitive diagnosis is paramount. The Coeliac Research Fund diagnostic postcard provides guidelines for diagnosis of coeliac disease. Contact your state Coeliac Society for a copy of the postcard or download a copy here.

The tests for coeliac disease are simple – just follow the steps below…

1. Keep eating gluten
Do not commence a gluten free diet prior to being tested for coeliac disease. If a gluten free diet has been adopted, the tests used to diagnose coeliac disease will be unreliable, and may be falsely negative.

If gluten has been removed from the diet, a normal diet must be resumed for at least six weeks prior to testing. During this ‘gluten challenge’, four slices of wheat based bread (or equivalent) should be consumed each day (for adults). A gluten challenge can be a daunting prospect for some people. Keep in mind that symptoms may be fairly severe for the first few days of the challenge, but they may settle with time in most people.

2. Blood Tests are used for screening
Blood tests (coeliac serology) are used to initially screen for coeliac disease. Coeliac serology measures blood antibody levels, which are typically elevated in those with untreated coeliac disease. The antibodies measured include:

• Anti-tissue transglutaminase antibodies (tTG)
• Deamidated gliadin peptide (DGP) IgA and IgG tests are now being used by a number of facilities in place of the old Anti-gliadin antibodies (AGA). The DGP IgG performs about as well as the tTG IgA. The DGP IgG can pick up individuals with coeliac disease even if they are deficient in IgA antibody and also shows particular utility in infants for detection of coeliac disease.
• Anti- endomysial antibodies (EMA). EMA is similar to tTG and is less used nowadays.

Total IgA should also be measured to exclude IgA deficiency. Approximately 2% of people with coeliac disease are IgA deficient, rendering the tTG IgA test unreliable in these people.

A diagnosis of coeliac disease SHOULD NOT be made on the basis of blood test alone. A significant level of positive coeliac blood test results may be false. If any of the coeliac serology antibody tests return a positive result, this suggests coeliac disease and warrants a biopsy of the small intestine.

3. A Small Bowel Biopsy is essential
A diagnosis of coeliac disease can only be made by small bowel biopsy. The optimal assessment for coeliac disease includes five biopsies taken during gastroscopy, one from the very beginning of the small intestine (the first part of the duodenum), and four further biopsies from sites scattered over the first 10-30cm of the small bowel (two biopsies from the 2nd and also the 3rd part of the duodenum). A gastroscopy is a simple day procedure done under light anaesthetic sedation that takes about 10 minutes. In the majority of cases, the bowel damage present in those with untreated coeliac disease is not visible to the naked eye. The biopsies are examined under a microscope to confirm the presence of classic small bowel changes.

Gene Testing (HLA genes)
Gene testing is presently available through pathology laboratories (by blood test or buccal (cheek) swab). People are born with the genetic predisposition to develop coeliac disease. Environmental factors then play a role in triggering the disease.

Over 99% of people affected by coeliac disease possess at least one of the genes that encode HLA DQ2 or HLA DQ8. The genes most often associated with coeliac disease are called HLA DQA1*05, and HLA DQB1*02, which together encode the HLA DQ2 protein and are often inherited together. The genes encoding HLA DQ8 are called HLA DQA1*03 and HLA DQB1*0302. The risk of coeliac disease is greater in those with the HLA DQ2 genes compared with the HLA DQ8 genes. The risk is no greater in people who have both HLA DQ2 and DQ8 than if they just had one copy of the HLA DQ2 genes.

Only one in 30 people who carry a coeliac gene will develop coeliac disease. Hence the gene test alone cannot diagnose coeliac disease. A gluten free diet should never be commenced based on a positive gene test. A gluten free diet should only be started after confirmation of coeliac disease by small bowel biopsy.

The gene test is useful for excluding coeliac disease – a negative gene test effectively rules out coeliac disease. As the gene test is not dependent on gluten intake, it can be used when people have already commenced a gluten free diet. If the gene test returns a positive result, a gluten challenge to allow diagnostic tests will be required to confirm coeliac disease.

For more information download our coeliac disease diagnosis brochure here. Or contact us to request a copy by mail.