Lucan · Conditions

Coeliac disease

gastroenterology6 free questions

Australian guidance: GESA Coeliac Disease Guidelines

1. Definition and epidemiology

Coeliac disease is a chronic immune-mediated enteropathy of the small bowel triggered by dietary gluten (wheat gliadins and related proteins in rye, barley and oats) in genetically susceptible individuals, producing inflammation and progressive tissue damage. At least 1 in 70 Australians have coeliac disease, making it one of the most prevalent chronic gastrointestinal conditions in the country. Approximately 80% of affected individuals remain undiagnosed, meaning the burden of disease is substantially underestimated in clinical settings. The condition affects all ages and both sexes, though females are diagnosed more often than males.

2. Pathophysiology

Gluten is the protein complex found in wheat (gliadin fraction), rye and barley. Following ingestion, gliadin peptides cross the intestinal epithelium and are deamidated by tissue transglutaminase 2 (tTG-2) in the lamina propria. Deamidated gliadin peptides bind with high affinity to HLA-DQ2 or HLA-DQ8 molecules on antigen-presenting cells, which activate CD4+ T-helper lymphocytes in a Th1-polarised inflammatory cascade. Cytokines including interferon-gamma and tumour necrosis factor drive crypt hyperplasia, accelerated enterocyte turnover and intraepithelial lymphocytosis. The structural result, graded by the Marsh classification from I (lymphocytosis only) through IIIc (total villous atrophy), is a dramatic reduction in absorptive surface area causing malabsorption of fat, fat-soluble vitamins (A, D, E, K), iron, folate, calcium and, in severe disease, vitamin B12. Anti-tTG-2 IgA autoantibodies are produced as a byproduct of the inflammatory response; they serve as the primary diagnostic marker and may contribute to extraintestinal manifestations including dermatitis herpetiformis.

3. Clinical presentation and diagnostic criteria

Presentation is highly variable. The most common symptoms are fatigue, diarrhoea, weight loss, abdominal pain, bloating and indigestion, but a substantial proportion of patients have no gastrointestinal symptoms at all. Classical coeliac disease (more common in young children) presents with chronic diarrhoea, steatorrhoea, abdominal distension and failure to thrive. In adults and older children, atypical and silent presentations predominate.

Clinicians should actively screen for coeliac disease in the following situations:

All children and adolescents with suspected coeliac disease should be referred to a paediatrician for specialist-led assessment and management.

Noncoeliac gluten sensitivity (gluten intolerance) is a distinct condition in which small amounts of wheat-based products are usually tolerated and ingestion does not cause the long-term intestinal damage seen in coeliac disease.

4. Investigations and AU-specific cutoffs

Serology must be performed while the patient is consuming gluten at a level equivalent to at least 4 slices of wheat-based bread per day (8 to 10 g of gluten daily). Testing on a gluten-free diet is not valid and will yield false-negative results.

First-line serology includes two tests ordered together:

  1. IgA anti-tissue transglutaminase (anti-tTG IgA) and anti-deamidated gliadin peptide antibodies, which are highly sensitive and specific for coeliac disease
  2. Total serum IgA to exclude IgA deficiency, which affects 2 to 3% of coeliac patients and causes false-negative IgA-based antibody results; IgG-class tests should be substituted when IgA deficiency is confirmed

If serology is positive, endoscopic biopsy of the duodenal mucosa is required to confirm the diagnosis. GESA recommends at least four biopsies (two from the duodenal bulb and two from the second or third part of the duodenum). Histological confirmation rests on the triad of intraepithelial lymphocytosis, crypt hyperplasia and villous blunting.

HLA-DQ2 and HLA-DQ8 gene testing is not appropriate as a screening test because these alleles are present in approximately 50% of the Australian population. Their clinical role is in exclusion: a negative HLA test reliably rules out coeliac disease and can be used when a patient is already on a gluten-free diet and is unwilling or unable to undergo a gluten challenge for serology.

At the time of diagnosis, the following baseline investigations are indicated per eTG and GESA guidance: full blood count, iron studies and ferritin, folate, vitamin B12, vitamin D (25-hydroxycholecalciferol), calcium, thyroid function tests, and liver biochemistry. Bone mineral density by DEXA scan should be performed in adults to screen for osteopenia or osteoporosis.

5. Management

The only proven treatment for coeliac disease is a strict, lifelong gluten-free diet. This means complete elimination of all foods containing wheat, rye, barley and oats. All patients should be referred at diagnosis to an Accredited Practising Dietitian experienced in coeliac disease; the diet is complex and often overwhelming, and dietitian input is considered standard of care in both eTG and GESA guidelines. Patients should be directed to Coeliac Australia (membership requires a signed medical practitioner confirmation) for ongoing product guidance and peer support.

Many sources of gluten are non-obvious. Patients must be counselled about hidden gluten in sauces, gravies, condiments, confectionery, beer and medications. Clinicians should check medications for gluten content using MIMS, which flags gluten-free preparations. Even small amounts of gluten cause ongoing intestinal damage regardless of the presence or absence of symptoms; dietary adherence cannot be relaxed asymptomatically.

Newly identified nutritional deficiencies must be treated promptly. If dietary adherence is confirmed and antibody levels are not improving after 9 to 12 months, referral to a dietitian for thorough dietary review is the first step. If a patient has adhered strictly and still shows no response after 12 months, referral to a gastroenterologist is required to consider refractory coeliac disease and assess for immunosuppressive therapy.

Thyroid function should be tested at diagnosis given the association with autoimmune thyroid disease. Liver biochemistry should also be obtained as coeliac disease is rarely associated with abnormal liver function.

6. Pharmacology and AU PBS notes

There are no PBS-listed disease-modifying pharmacological agents for coeliac disease itself. Drug therapy is directed at complication management:

7. Complications and monitoring

Undiagnosed and untreated coeliac disease is associated with increased overall mortality, a modest increase in risk of gastrointestinal malignancy and lymphoma, osteoporosis, iron deficiency anaemia and adverse reproductive outcomes including miscarriage.

Refractory coeliac disease (RCD) is defined as persistent or recurrent malabsorptive symptoms with villous atrophy on biopsy despite more than 12 months of strict dietary adherence, after excluding inadvertent gluten ingestion. RCD type II involves an aberrant clonal intraepithelial lymphocyte population and is a premalignant condition with significant risk of progression to enteropathy-associated T-cell lymphoma (EATL), a rare but aggressive malignancy. Small bowel adenocarcinoma risk is also elevated in longstanding disease.

Hyposplenism occurs in a subset of patients, increasing susceptibility to infection with encapsulated organisms such as Streptococcus pneumoniae and Neisseria meningitidis; pneumococcal and annual influenza vaccination are recommended.

Microscopic colitis is associated with coeliac disease. Patients who continue to experience diarrhoea despite strict adherence to a gluten-free diet should be referred for colonoscopy to exclude this.

Monitoring schedule per eTG and GESA guidance:

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Written for Australian practice and grounded in the guidance named above. Study material only — not medical advice. Always check against current guidelines.