Diagnosing Coeliac Disease
Untreated, coeliac disease has significant health implications. It is important to be diagnosed and managed properly.
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 already been adopted, the tests used to diagnose coeliac disease are unreliable, and can 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’, a minimum of four slices of wheat based bread (or equivalent) should be consumed each day (for adults) (2 slices of wheat based bread each day for children). It is important the gluten challenge is carried out properly to ensure reliable testing results.
2. Blood Tests are used for screening
Blood tests (coeliac serology) are used to screen for coeliac disease. ‘Coeliac serology’ measures antibody levels in the blood which are typically elevated in people with untreated coeliac disease. The antibodies measured include:
- Anti-tissue transglutaminase antibodies (tTG-IgA)
- Deamidated gliadin peptide (DGP) IgA and IgG. This has superceded the older, less accurate anti-gliadin antibody (AGA) test. The DGP performs similarly to the tTG test.
The DGP IgG can pick up individuals with coeliac disease even if they are deficient in IgA antibody. It may also be useful as a screening test in infants.
- Anti-endomysial antibodies (EMA). EMA is similar to tTG but is less commonly tested nowadays.
Total immunoglobulin (IgA) levels are often measured to exclude the 3% of people with coeliac disease who are deficient in IgA. IgA deficiency renders the tTG-IgA test unreliable.
In children under the age of four years the tTG-IgA test is also less reliable. As antibody levels can fluctuate in children, it is suggested the antibody tests be performed on two occasions three months apart.
Importantly, a diagnosis of coeliac disease SHOULD NOT be made on the basis of a blood test alone. A positive blood test always needs to be followed by a small bowel biopsy to confirm the diagnosis.
3. A Small Bowel Biopsy is essential
A diagnosis of coeliac disease can only be made by demonstrating the typical small bowel changes of coeliac disease (villous atrophy). This involves a gastroscopy procedure in which several tiny samples (biopsies) of the small bowel are taken. 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 villous atrophy.
Gene Testing (HLA genes)
Gene (HLA) testing is a useful test in select cases when the diagnosis of coeliac disease is unclear. This can occur if the blood or small bowel biopsy results are difficult to interpret, or if adequate gluten was not being consumed to make the test reliable. It is performed on a blood test or cheek (buccal) scraping and can be ordered through your local doctor.
Over 99% of people affected by coeliac disease possess either HLA DQ2, HLA DQ8, or parts of these genes. A negative gene test for HLA DQ2 and HLA DQ8 therefore effectively rules out a diagnosis of coeliac disease. The gene test on its own cannot diagnose coeliac disease – only one in 30 people who possess HLA DQ2 or HLA DQ8 will develop coeliac disease.A gluten free diet should only be started after confirmation of coeliac disease by small bowel biopsy.
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 is negative for HLA DQ2 and HLA DQ8 then coeliac disease can be ruled out. If the gene test is positive for HLA DQ2 or HLA DQ8, then a gluten challenge followed by small bowel biopsy will be required to test for coeliac disease.
Beware of unorthodox diagnosis techniques
There are a number of tests and treatments for allergy, intolerance and coeliac disease that are used in the absence of any scientific rationale. These tests and treatments have been shown to be unreliable when subjected to careful study. Unproven testing methods provide misleading results, delay correct diagnoses and lead to unnecessary and ineffective treatment. The Australasian Society of Clinical Immunology and Allergy (ASCIA) advise against the use of such tests for diagnosis or to guide medical treatment. Such methods may include stool-based tests, Vega testing, iridology, hair analysis or the inappropriate use of tests for food-specific immunoglobulin. For a full list and more information about unorthodox tests and treatments, visit the ASCIA website: www.allergy.org.au.
The benefits of diagnosis
As coeliac disease is a serious medical condition with lifelong implications, a definitive diagnosis is essential. The gluten free diet is not a trivial undertaking and involves lifestyle changes and learning new skills such as reading and interpreting food labels. It should only be undertaken after the diagnosis of coeliac disease has been properly medically established.
- A strict gluten free diet has positive implications for health by reducing the long-term risks associated with coeliac disease. People who have been properly medically diagnosed are more likely to maintain the strictness required to remain healthy.
- By obtaining a proper diagnosis, you can be assured that your symptoms are caused by coeliac disease (and should therefore improve once the gluten free diet is established) and not by another more sinister condition.
- As a genetic condition, there could be implications for your family once a diagnosis of coeliac disease is made. Following a diagnosis of coeliac disease, immediate family members should be screened.
- On diagnosis of coeliac disease, screening for complications and associated conditions such as osteoporosis or autoimmune diseases should occur. Being diagnosed appropriately will ensure this important medical assessment takes place.
- Following a proper diagnosis, a dietitian will be more likely to consider additional food intolerance if symptoms persists despite strict adherence to a gluten free diet.
- In the future, it is likely that any potential non-dietary therapy for coeliac disease, such as a therapeutic vaccine, will only be available to those who have coeliac disease properly proven by biopsy.
- Adjusting to the gluten free diet may seem difficult at first but as your knowledge and confidence grows, managing the diet becomes easier. Advice from a specialist dietitian is invaluable and can greatly enhance the enjoyment to be had from a gluten free lifestyle.