Diagnosing coeliac disease – the key facts

Coeliac disease is common and treatment improves outcomes 

• Coeliac disease is an autoimmune disorder occurring in genetically susceptible individuals that results in an abnormal immune response to dietary gluten. 
• Over 1 in 70 Australians are affected, but the broad clinical presentation means that coeliac disease is often overlooked – 4 out of 5 Australians remain undiagnosed. 
• Symptoms often go unrecognised or patients may be truly asymptomatic. Targeted screening of at-risk patients is the most effective way to detect coeliac disease. 
• Untreated coeliac disease is associated with a range of complications, including nutrient deficiencies; premature osteoporosis; abnormal liver function; higher rates of other autoimmune diseases, such as thyroid disease; infertility and poorer pregnancy outcomes; sepsis; and some forms of malignancy, especially lymphoproliferative disorders, such as lymphoma. 
• Strict removal of dietary gluten – a protein found in wheat, rye, barley and oats – can arrest the damaging inflammatory immune response caused by gluten and is important to reduce morbidity and mortality. 

Symptoms and signs that should prompt testing for coeliac disease: 

• Chronic or intermittent gastrointestinal symptoms, such as diarrhoea, constipation, abdominal pain, bloating or flatulence 
• Prolonged fatigue (“tired all the time”) 
• Iron deficiency anaemia or nutritional deficiency 
• Sudden or unexpected weight loss 
• Dental enamel defects or mouth ulcers 
• Low-trauma fracture or premature osteoporosis 
• Unexplained infertility or recurrent miscarriage 
• Abnormal liver function tests (especially elevated transaminases) 
• Peripheral neuropathy, ataxia or epilepsy 

High-risk associations that should prompt testing for coeliac disease:

• Family history of coeliac disease (10-20% risk) 
• Autoimmune thyroid disease 
• Type 1 diabetes 
• Other autoimmune disease, e.g. Addison’s disease, Sjogren’s syndrome, autoimmune liver disease 
• Dermatitis herpetiformis (an itchy, blistering skin condition) 
• Immunoglobulin A (IgA) deficiency 
• Down’s syndrome 
• Turner syndrome

How to test for coeliac disease: 

1. Confirm your patient is consuming a gluten- containing diet for accurate results (see box below for management if they are already following a gluten free diet). 
2. Request coeliac disease serology, 

• Transglutaminase-IgA (tTG-IgA) and deamidated gliadin peptide-IgG (DGP-IgG) 

• Transglutaminase-IgA (tTG-IgA) with total IgA level (to exclude the 2-3% of people with coeliac disease who are IgA deficient) 

3. In select cases, HLA-DQ2/8 genotyping may be performed on blood or buccal scrape. 

The HLA DQ2/8 gene test can be useful when screening high-risk individuals,  e.g. those with a positive family history, to guide the need for further clinical work-up. 

How to interpret these tests:

• If tTG-IgA and/or DGP-IgG is positive refer to a gastroenterologist for confirmatory small bowel biopsy. Serology alone is insufficient to diagnose coeliac disease. 
• A positive HLA-DQ2/8 gene test is not diagnostic of coeliac disease in isolation (approximately half of the general population are positive). 
• A negative HLA-DQ2/8 gene test has strong negative predictive value (<1% likelihood of coeliac disease being present) and means coeliac disease can be excluded. 
• If coeliac serology is negative but the patient is symptomatic and positive for HLA-DQ2 and/or HLA-DQ8 then consider referral to a gastroenterologist for further work-up. 
• A HLA-DQ2 and/or HLA-DQ8 positive relative with normal coeliac serology is at-risk for future development of coeliac disease and follow-up is warranted. Repeat screening is recommended if they become symptomatic (suggestive symptoms indicated over the page). 

If your patient is following a gluten free diet prior to testing:

Option 2 – If your patient is reluctant or unable to complete a gluten challenge, offer HLA-DQ2/8 gene testing. If HLA DQ2/8 gene testing is negative coeliac disease can be safely excluded. If it is positive, then option 1 is the only feasible diagnostic approach. 

Once coeliac disease has been diagnosed:

1. Refer to a dietitian with a special interest in coeliac disease for nutritional education.
2. Download the chronic disease management template ​​​​​​​ to guide ongoing follow-up.
3. Provide a Coeliac Australia membership referral letter for ongoing support.

References

1. Anderson RP. Aust Fam Physician. 2005 Apr;34(4):239-42;
2. Kenrick K and Day AS. Aust Fam Physician. 2014 Oct;43(10):674-8;
3. Steele R et al. Postgrad Med J. 2011 Jan;87(1023):19-25;
4. Tye-Din JA et al. Intern Med J. 2015 Apr;45(4):441-50;
5. NICE (UK) guidelines: Coeliac disease: recognition, assessment and management (2015). www.nice.org.uk/guidance/ng20