Clinical opal – Is it coeliac disease?
Amanda is a 26 year old speech pathologist who presents to you with longstanding gastrointestinal symptoms. She describes frequent episodes of diarrhoea and abdominal bloating and wonders whether it may be “related to gluten”.
On further questioning, Amanda is otherwise asymptomatic. She has no significant PMH and her only regular medication is the oral contraceptive pill. She is a non-smoker and drinks minimal alcohol. She has known family history of coeliac disease.
What pathology tests would you order to investigate her for possible coeliac disease?
Coeliac disease is an autoimmune condition triggered by the ingestion of gluten. It is characterised by chronic inflammation of the small intestinal mucosa and leads to a range of gastrointestinal and extra-intestinal manifestations. Coeliac disease is challenging to diagnose due to its varied and often subtle presentation.
Pathology testing for coeliac disease involves the use of coeliac serology and/or genetic testing.1 Coeliac serology consists of the transglutaminase (tTG) and deamidated gliadin peptide (DGP) antibody tests. In practice, both tests have >85% sensitivity and >90% specificity. The anti-endomysial antibody (EMA) test is not routinely performed but can be used as a confirmatory test.
Points to consider when interpreting coeliac serology include:
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Positive coeliac serology in isolation is insufficient for the diagnosis of CD - histological evaluation of duodenal biopsies is required for definitive diagnosis
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The higher the serology titre, the greater the PPV for CD
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CD serology has a false negative rate of 10–15% - this is most commonly related to the patient being on a gluten free diet, or immunosuppression. Negative serology does not exclude the diagnosis of CD in patients with risk factors and a higher pre-test probability for CD, and further assessment should be considered.
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Comparing titres from different laboratories can be misleading due to the use of different assays.
Genetic testing for CD with the HLA DQ2/DQ8 gene test has a role but should be restricted to specific circumstances. Genetic testing is very useful as a rule-out test - as >99% of patients with CD carry one or other gene, a negative test effectively excludes CD. However, a positive test is less helpful and cannot be used to diagnose CD, as at least 40-50% of the population are asymptomatic carriers. Furthermore, HLA typing is expensive, so it is important to use it prudently.
References
1. Tye-Din J. Interpreting tests for coeliac disease: Tips, pitfalls and updates. Aust J Gen Pract. 2018 Jan-Feb;47(1-2):28-33.
Simon is a GP based in Newcastle, NSW, and a senior medical educator with Medcast. He also has medical education roles with the RACGP and GPSA.
Over the past three decades, Simon has worked in clinical and educational roles in NSW and the NT, as well as in the Republic of Ireland. He has published over 75 peer reviewed journal articles, and in 2018 received the RACGP Corliss award for his contribution to medical education.
Simon is passionate about high quality education and training. He has particular interests in GP supervisor professional development and the rational use of tests and medicines. He is a proud member of Doctors for the Environment. He spends his spare time drinking craft beer and pretending that he is a musician in the Euthymics, an all-GP band.
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