Decision support only — not a substitute for gastroenterology, specialist dietetics, pathology review or local policy. Keep gluten in the diet until diagnostic testing is complete unless illness makes this unsafe. Correct deficiencies to measured need; verify doses, vaccine eligibility and MBS criteria locally.
1 The diagnostic path
Coeliac disease is a systemic immune-mediated disorder; small-bowel enteropathy is its defining lesion, not its only clinical expression. The easiest way to make it difficult to diagnose is to prescribe a gluten-free diet before testing. Symptoms may improve for several reasons; that response does not establish the diagnosis.
Symptoms, associated condition or first-degree relative warrants testingGI symptoms · iron deficiency · weight loss/fatigue · T1DM/thyroid disease · osteoporosis · abnormal LFTs · dermatitis herpetiformis
Currently eating a gluten-containing diet?
YES → serology first
NO / ALREADY RESTRICTINGDo HLA-DQ2/DQ8 first. A negative result makes coeliac disease highly unlikely. A positive result is common and does not diagnose it. If confirmation matters, arrange a supervised gluten challenge: Australian advice is approximately 10 g gluten/day (about 4 slices of wheat bread) for at least 6 weeks, then serology ± biopsy. Tailor if symptoms are severe. COELIAC AUSTRALIA
1 · SEROLOGY
Australian one-step option: tTG-IgA + DGP-IgG (MBS 71164). Alternative: tTG-IgA + total IgA; if IgA deficient, use IgG-based tTG/DGP. CA MAC
Negative but suspicion remains: check gluten intake, IgA deficiency and immunosuppression; refer for biopsy where malabsorption or strong clinical suspicion persists.
2 · CONFIRM
Adults in Australia: positive serology usually proceeds to UGI endoscopy while still eating gluten. Take 4 biopsies from D2 + 2 from the bulb; normal endoscopic appearance does not exclude disease. ESSCD 2025
Histology: with positive serology, >25 IELs/100 epithelial cells plus crypt hyperplasia ± villous atrophy supports Marsh 2–3 coeliac disease. Correct orientation matters; villous atrophy alone has a differential. BSG 2026
3 · AFTER CONFIRMATION
Start lifelong strict gluten-free diet with an Accredited Practising Dietitian. Establish baseline nutrition, bone and autoimmune status.
Screen first-degree relatives with serology while they eat gluten. HLA can refine future testing when the result is negative.
2 Who should be tested — active case-finding
About 1 in 70 Australians have coeliac disease, yet roughly 4 in 5 remain undiagnosed. Classical malabsorption is only one phenotype; case-finding among symptomatic people and high-risk groups is more useful than untargeted population screening. COELIAC AUSTRALIA
Offer serology
- GutPersistent unexplained diarrhoea, bloating, abdominal pain, constipation, nausea/vomiting or adult IBS.
- SystemicUnexplained iron/B12/folate deficiency, prolonged fatigue, weight loss, faltering growth or severe recurrent aphthae.
- AutoimmuneT1DM or autoimmune thyroid disease at diagnosis.
- FamilyAll first-degree relatives; risk is approximately 1 in 10. COELIAC AUSTRALIA
Lower threshold
- BonePremature osteoporosis, osteomalacia or fragility fracture.
- NeuroUnexplained peripheral neuropathy or ataxia.
- ReproUnexplained subfertility or recurrent miscarriage.
- OtherCryptogenic transaminitis, dental enamel defects, Down or Turner syndrome, selective IgA deficiency.
Phenotype traps
- WeightOverweight or obesity does not exclude coeliac disease.
- AgeIt can present in older adults; late diagnosis deserves attention to bone loss and malignancy red flags.
- SexMen are diagnosed less often and are easy to overlook.
- SerologyAustralian guidance cites a 10–15% false-negative rate. A convincing syndrome can outrank one negative result.
3 Read the tests without overcalling them
| Result / situation | What it means | Registrar move |
|---|
| tTG-IgA positive | Probability rises with titre; low titres have false positives, including autoimmune and liver disease. | Keep gluten in diet; gastro referral for biopsy. EMA can resolve selected ambiguous results but is not routinely required by ESsCD. |
| IgA deficient | tTG-IgA may be falsely negative. | Use IgG tTG and/or DGP. Negative IgG assays do not safely exclude disease when malabsorption is convincing; biopsy. |
| HLA-DQ2/8 negative | Coeliac disease is highly unlikely; HLA is useful as a rule-out test. | Reconsider the diagnosis. Do not use HLA as population screening or proof of disease: nearly half the community carries a permissive genotype. |
| Positive serology, normal villi | Potential coeliac disease, false-positive serology, inadequate gluten exposure or sampling/orientation error. | Review diet, assay, biopsy number/site and pathology; consider HLA. If potential disease is confirmed, use specialist follow-up rather than an automatic lifelong label; a dietitian-guided GFD trial may be reasonable when symptomatic. BSG 2026 |
| Villous atrophy, negative serology | Seronegative coeliac is possible but is a diagnosis of exclusion. | Check IgA/gluten exposure; exclude Giardia, CVID, Crohn disease, autoimmune enteropathy and drug injury (notably olmesartan). Obtain HLA and expert pathology review. Marsh 3 histology + permissive HLA + improvement on GFD can support the diagnosis; response alone cannot. BSG 2026 |
Adult no-biopsy diagnosis: evidence has moved; Australian implementation has not fully followed
- EuropeESsCD 2025 conditionally permits diagnosis in selected adults <45 years with tTG-IgA ≥10× ULN, confirmed on a second sample, through secondary care and without red flags. ESSCD 2025
- UKBSG 2026 conditionally permits a no-biopsy diagnosis in symptomatic adults with tTG-IgA ≥10× ULN, assessed in secondary care after shared decision-making. Its headline recommendation does not specify an age ceiling or mandatory second sample. BSG 2026
- EvidenceSHIHA 2024 pooled 18 studies/12,103 adults: sensitivity 51%, specificity 100%, PPV 98% in studied populations. PPV still depends on pre-test probability and assay performance.
- AustraliaCurrent Coeliac Australia guidance says positive serology alone is insufficient, citing tTG assay variation and limited EMA availability. Use biopsy as the default adult pathway unless a gastroenterologist applies a validated local protocol.
4 Treatment — food is the disease-modifier
Strict, lifelong gluten-free diet
- ExcludeWheat, rye and barley; control cross-contact in food preparation, eating out and shared kitchens.
- LabelIn Australia, “gluten free” means no detectable gluten. Read the ingredient and mandatory allergen summary statements.
- DietitianCoeliac-experienced APD at diagnosis and again if symptoms, serology or diet quality drift.
- AvoidNo “mostly gluten-free”, cheat days or empiric GFD before testing.
Build a nutritionally decent diet
- CorrectIron, folate, B12, vitamin D, calcium and other measured deficiencies; severe malabsorption may need broader replacement.
- QualityProtect fibre, wholegrain intake and cardiometabolic health. Many packaged GF foods are lower in protein/fibre and higher in sugar or fat.
- LactoseTemporary restriction only if symptomatic secondary lactase deficiency; retry after mucosal recovery.
- DrugsNo approved medicine replaces the GFD. Supplements and refractory-disease therapy address consequences or selected complications.
Oats — Australian update
- 2026Coeliac Australia now supports an individual discussion about trialling pure, uncontaminated oats. CA OATS 2026
- CatchOat products cannot be labelled “gluten free” under FSANZ rules. “Wheat free”, “pure” and “organic” do not guarantee freedom from rye/barley contamination.
- SelectNo “may contain” wheat/rye/barley; check manufacturer cross-contact testing. Introduce gradually with clinical follow-up.
- AveninA minority react. HARDY 2025 found immune/symptom responses in some adults, usually without sustained enteropathy; 1/29 showed a wheat-like inflammatory response.
5 Baseline work-up and follow-up
| When | Clinical review | Tests / prevention | Escalate when |
|---|
| At diagnosis | Symptoms, weight/BMI, diet and access, mental health, pregnancy plans; APD education; discuss first-degree relative screening. | FBC, ferritin/iron, B12, folate, LFT, albumin, Ca/PO₄, 25-OH-D, TSH; add Mg/Zn/Cu with substantial malabsorption. Review vaccines. Assess bone health. | Severe malnutrition, major electrolyte disturbance, bleeding, marked weight loss, hypoalbuminaemia or malignancy features. |
| 4–6 months | Symptom trajectory, practical adherence, cross-contact, diet adequacy and coping; physician + dietitian where possible. | Repeat initially abnormal laboratories. Serology may still be positive; direction matters more than one early value. | No improvement, worsening diarrhoea/weight loss or new deficiency. |
| 12 months | Symptoms, dietitian review, weight and associated autoimmune disease. | tTG/DGP using a comparable assay; repeat abnormal nutrition/LFT tests. ESSCD PART 2 | Persistently high serology, little titre fall, red flags or unresolved biochemical malabsorption. |
| 24 months → q1–2 y | Tailor to adherence, education, symptoms and complication risk. | TSH; serology and nutrient tests as indicated. Repeat DXA according to baseline result and osteoporosis risk. | Relapse after initial response, anaemia, diarrhoea, pain, fever/night sweats, obstruction or unexplained weight loss. |
Bone
- AU adviceCoeliac Australia recommends baseline DXA for all diagnosed adults; a Medicare rebate applies to medically diagnosed coeliac disease.
- EuropeESsCD 2025/26 favours risk-stratified DXA. Prioritise fracture, low BMI, malabsorption, older age, menopause/andropause and steroid exposure.
Serology is a smoke alarm
- PositivePersistent elevation supports ongoing gluten exposure or active disease.
- NegativeDoes not prove mucosal healing or perfect adherence. Symptoms can also settle before the villi recover.
- BiopsyRepeat for persistent/relapsing symptoms, red flags, deficiencies or persistent seropositivity. Routine re-biopsy in a well adult is debated; if chosen, allow about 24 months.
Vaccines and splenic function
- RoutineKeep influenza, COVID-19 and age/risk-based vaccines current.
- PneumococcalCoeliac Australia and BSG 2026 advise pneumococcal vaccination for adults with coeliac disease. In Australia, choose product/timing and check NIP eligibility against the live Handbook.
- HypospleniaCoeliac disease can cause functional hyposplenia. If recognised, follow the Australian Immunisation Handbook schedule for pneumococcal, MenACWY, MenB and Hib.
- FundingRecommended and NIP-funded are not synonymous; verify current eligibility.
6 Persistent symptoms on a gluten-free diet
Ongoing gluten exposure, intentional or inadvertent, accounts for up to 80% of persistent symptoms in reported cohorts. Refractory coeliac disease is rare. An uncertain original diagnosis and common overlapping disorders should be worked through before that label appears in the notes. ESSCD PART 2
Stepwise review
- 1 · ProveRetrieve original serology, endoscopy and histology; review specimen adequacy, gluten exposure and HLA if uncertainty remains.
- 2 · ExposeSpecialist dietitian review for hidden gluten/cross-contact; repeat serology. Gluten-immunogenic peptide testing can be an adjunct, not a standalone verdict.
- 3 · Re-scopeIf symptoms or villous atrophy persist ≥12 months despite credible adherence, repeat biopsies and reassess histology.
- 4 · ImageWeight loss, pain, obstruction, bleeding, fever or hypoalbuminaemia: evaluate small bowel/lymphoma with specialist-directed CT/MR enterography, capsule or enteroscopy.
More common alternatives
- DietaryOngoing gluten; secondary lactose intolerance; FODMAP-related symptoms.
- FunctionalIBS or disorder of gut–brain interaction after mucosal healing; a dietitian-led low-FODMAP trial may help selected patients.
- Gut diseaseMicroscopic colitis, IBD, SIBO, Giardia, bile-acid diarrhoea or documented exocrine pancreatic insufficiency.
- OtherDrug enteropathy, CVID, thyroid disease, eating disorder, anxiety/depression or malignancy.
Refractory coeliac disease (RCD) — tertiary-centre diagnosis
- DefinitionPersistent or recurrent symptoms plus villous atrophy after ≥12 months of a strict GFD, after gluten exposure and other causes have been excluded. ESSCD PART 2
- Type IPhenotypically normal intraepithelial lymphocytes; better prognosis. Nutrition support and specialist anti-inflammatory/immunosuppressive therapy.
- Type IIAberrant/clonal IEL population; high EATL risk and poor prognosis. Flow cytometry/T-cell clonality, cross-sectional small-bowel assessment and expert gastro-haematology care.
- NeverDo not diagnose RCD from symptoms alone or escalate immunosuppression before dietary exposure, misdiagnosis, infection and lymphoma have been addressed.
7 Related phenotypes and useful distinctions
Dermatitis herpetiformis
- PatternIntensely pruritic grouped papulovesicles, classically elbows, knees, buttocks and scalp.
- ConfirmDirect immunofluorescence of uninvolved perilesional skin for granular IgA; coordinate gut evaluation.
- TreatLifelong GFD. Dapsone controls skin rapidly but does not heal the enteropathy; check G6PD, FBC and LFTs and monitor for haemolysis/methemoglobinaemia.
Wheat allergy
- MechanismIgE-mediated; immediate urticaria, angioedema, bronchospasm, vomiting or anaphylaxis.
- TestAllergy history, wheat-specific IgE/skin testing and specialist challenge where appropriate.
- DifferenceDoes not produce the coeliac serology–villous injury pattern.
Non-coeliac wheat sensitivity
- Before labelExclude coeliac disease while eating gluten and exclude wheat allergy.
- No markerNo validated diagnostic blood test. Symptoms overlap with IBS and may reflect wheat fructans rather than gluten.
- DietUse a structured dietitian-led elimination/rechallenge. A needless lifelong restriction has cost, nutrition and social harms.
Primary sources. Coeliac Australia Medical Advisory Committee:
Australian burden,
testing pathway,
gluten challenge,
monitoring and
oats update (accessed Aug 2026). Penny HA et al.
British Society of Gastroenterology guidelines on the diagnosis and management of coeliac disease in adults. Gut 2026; doi:10.1136/gutjnl-2025-337747. Al-Toma A et al.
ESsCD 2025 Updated Guidelines, Part 1: Diagnostic Approach. UEG Journal 2025;13:1855–1886. Al-Toma A et al.
ESsCD 2025 Updated Guidelines, Part 2: Management, Follow-Up and Complex Disease Courses. UEG Journal 2026;14:e70195. Rubio-Tapia A et al.
ACG Clinical Guideline: Diagnosis and Management of Celiac Disease. Am J Gastroenterol 2023;118:59–76.
NICE NG20, updated 2024.
Australian Immunisation Handbook: asplenia/hyposplenia, updated Jun 2026. MBS pathology items
71163/
71164, fees updated Jul 2026.
Key evidence. Shiha MG et al.
Accuracy of the No-Biopsy Approach for Diagnosis of Celiac Disease in Adults: systematic review/meta-analysis. Gastroenterology 2024;166:620–630. Hardy MY et al.
Purified oat protein can trigger acute symptoms linked to immune activation in coeliac disease patients but not histological deterioration. Gut 2025;74:906–917. Elli L et al.
Guidelines for best practices in monitoring established coeliac disease in adults. Nat Rev Gastroenterol Hepatol 2024;21:198–215.
Caveats. This is an adult registrar sheet; paediatric no-biopsy diagnosis follows ESPGHAN criteria and specialist paediatric pathways. Australian assay performance and local gastroenterology protocols determine whether any adult no-biopsy pathway is safe. BSG no-biopsy and vaccination recommendations are UK guidance; implementation and funding differ in Australia. Coeliac Australia is a patient organisation advised by its Medical Advisory Committee, not a government guideline issuer. Food-labelling rules, MBS items, vaccine schedules and funding change; check live Australian sources. Recommendations are paraphrased.