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Testing for coeliac disease

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Coeliac serology testing

Step 01

Confirm your patient is consuming a gluten-containing diet for accurate results

Step 02

Request coeliac disease serology, specifically:

Transglutaminase-IgA (tTG-IgA) and deamidated gliadin peptide-IgG (DGP-IgG)
[Medicare Benefits Schedule (MBS) item number 71164, double antibody test – preferred, one-step approach]

Transglutaminase-IgA (tTG-IgA) with total IgA level (to exclude the 2-3% of people with coeliac disease who are IgA deficient)
[If the IgA level is low, perform the deamidated gliadin peptide-IgG (DGP-IgG). MBS item number 71163, single antibody test]

Tips about coeliac serology

Positive coeliac disease serology in isolation is insufficient for the diagnosis of coeliac disease. Advise your patient not to start a gluten‑free diet until diagnosis is confirmed by a specialist, even if the results of a serological test are positive.
The higher the titre of serology, the greater the positive predictive value for coeliac disease.
Coeliac disease serology has a false negative rate of 10–15%. Always check if your patient is on a gluten free diet or taking immunosuppressants.

Small bowel biopsy

Positive serology alone should not be used to diagnose coeliac disease. Examination and evaluation of biopsies taken from the small bowel is an important part of diagnosing coeliac disease. Multiple biopsies should be taken and microscopic examination is essential.

Remember:

Villous atrophy is suggestive of coeliac disease but can be due to other conditions. Other causes to consider, especially if coeliac disease serology is negative, include Giardia, common variable immunodeficiency, Crohn’s disease, tropical sprue, autoimmune enteropathy, cow’s milk protein intolerance and some medications (e.g. olmesartan).
A gluten free diet or immunosuppression can obscure changes of villous atrophy.
Correct biopsy processing and interpretation by a skilled pathologist is vital. When there is diagnostic uncertainty, review of the pathology can be informative.

Never recommend a gluten free diet until appropriate medical tests have taken place.
There is no room for an empirical trial of a gluten free diet as symptomatic improvement is NOT diagnostic of coeliac disease.

A note about paediatric testing

Although similar to adults, there are additional considerations when assessing children for coeliac disease. For children, a biopsy may not be necessary in every case, but the diagnosis of coeliac disease should be made by a specialist. Guidelines from the European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) suggest small intestinal biopsies can be avoided if children meet the following criteria:

tTG-IgA levels >10× upper limit of normal
A positive endomysial antibody (EMA) on a different blood sample
The utility of this approach in Australia is uncertain because of the limited availability of the EMA test, as well as intra-lab variation and lack of standardisation of the tTG assay. Further validation is warranted. The decision to make a non-biopsy diagnosis should only be made with specialist paediatric input.

Non-Coeliac Gluten
Sensitivity (NCGS) /’Gluten Intolerance’

Wheat or gluten in the diet is often incorrectly blamed as a cause of a variety of unpleasant symptoms. Work with your patients to help determine the genuine cause of symptoms and guide them to the best treatment for them.

Coeliac disease is an important cause of gluten sensitivity (or intolerance). It can be associated with serious medical problems so appropriate testing is essential.

There is no room for an empirical trial of a gluten free diet as symptomatic improvement is NOT diagnostic of coeliac disease.
Never recommend a gluten free diet until appropriate medical tests have taken place. A gluten challenge is required prior to testing if gluten has already been excluded from the diet.

If coeliac disease and other medical diagnoses have been excluded, Irritable Bowel Syndrome (IBS) may be a potential diagnosis. Dietary modification (in combination with other treatments) is often the first line of therapy for IBS. While gluten and wheat are often blamed, the malabsorption of fermentable sugars (FODMAPs) is a more likely culprit in those with IBS.