Dr Henry WeiGastroenterology & Endoscopy
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Coeliac disease: testing, diagnosis and follow-up

Test while the patient is eating gluten, confirm the diagnosis and arrange dietary and nutritional follow-up.

On this page

Author: Dr Henry Wei. Sources checked 15 October 2026.

In practice

Complete the diagnostic assessment before removing gluten

I check gluten intake and tTG-IgA before interpreting the result. Positive or clinically discordant findings need gastroenterology assessment before a lifelong gluten-free diet.

Guidance behind this advice

1. Recognise who needs testing

Consider coeliac disease with unexplained iron deficiency, chronic diarrhoea, persistent IBS-type symptoms, weight loss, early osteoporosis or unexplained liver-test abnormalities. Ask about family history, type 1 diabetes and autoimmune thyroid disease.

2. Choose and interpret the tests

Initial coeliac assessment
SituationPractical step
Eating glutenRequest tTG-IgA.
Strong suspicion despite negative serologyReview gluten intake and total IgA if it has not been reported. IgA deficiency can make initial tTG-IgA testing falsely negative; discuss specialist assessment.
Already gluten-freeReview old serology and histology. Negative HLA-DQ2/DQ8 can help exclude disease; a positive result does not confirm it.

3. Confirm before changing the diet

Ask the patient to continue gluten until assessment is complete. Refer with the actual antibody titre, assay upper limit, symptoms and gluten intake.

Duodenal biopsies are particularly useful with lower titres, uncertain findings or alarm symptoms.

Some international guidelines describe no-biopsy pathways for selected adults with very high titres, but these are not universally endorsed; any such diagnosis should follow local guidance and specialist assessment. Agree any gluten challenge with gastroenterology; children require paediatric assessment.

4. Support treatment and check recovery

Arrange an experienced dietitian and Coeliac New Zealand support. Check symptoms, weight, dietary adherence, serology and relevant deficiencies, including FBC, ferritin, folate and B12. Assess liver tests and bone health.

Persistent symptoms warrant review of gluten exposure and the original diagnosis, then consideration of IBS, lactose intolerance, microscopic colitis or other malabsorption. Refer persistent anaemia, weight loss, vomiting or concerning pain; repeat biopsy may be appropriate.

Clinical pearls

  • Coeliac disease may present with iron deficiency or abnormal liver tests without diarrhoea.
  • Improvement after avoiding wheat does not confirm coeliac disease.
  • Normalised antibodies do not by themselves confirm mucosal healing.
Diagrams for patient discussions
Explore the explanation

Understand the test before changing your diet

Choose a view
Explanatory diagram
Different tests answer different questionsThe sequence is planned while gluten is still in the diet. Blood antibodies An immune response signal Interpret with the laboratory report. Duodenal biopsy Microscopic tissue assessment Usually through gastroscopy. HLA gene test Can help exclude in selected cases A positive gene is not a diagnosis. Specialist review Results, gluten intake and history Agree the confirmation pathway. Do not start a gluten-free diet just to see whether a test improves.Different tests answer different questionsThe sequence is planned while gluten is still in the diet.Blood antibodiesAn immune response signalInterpret with the laboratory reportDuodenal biopsyMicroscopic tissue assessmentUsually through gastroscopyHLA gene testCan help exclude in selected casesA positive gene is not a diagnosisSpecialist reviewResults, gluten intake and historyAgree the confirmation pathwayDo not start a gluten-free diet just to see whether a test improves.

Blood, biopsy or gene test?

Coeliac disease is an immune response to gluten. Blood tests, tissue samples and sometimes a gene test contribute different information. Symptoms improving without gluten do not prove the diagnosis.

Simplified illustrations, not to scale. These show an example, not your own anatomy or test result.

Read every diagram explanation

Blood, biopsy or gene test?

Coeliac disease is an immune response to gluten. Blood tests, tissue samples and sometimes a gene test contribute different information. Symptoms improving without gluten do not prove the diagnosis.

Why keep eating gluten?

Reducing gluten can make blood tests and biopsies less reliable. If you have already stopped, I discuss the safest way to investigate rather than asking you to restart gluten without individual advice.

Why a biopsy may be useful

Gastroscopy can take tiny samples from the duodenum. The laboratory assesses villous architecture and other tissue changes. A normal camera appearance does not exclude microscopic disease.

After the diagnosis

A confirmed diagnosis leads to a gluten-free diet with dietitian support and follow-up. Symptoms, nutrition and blood results guide review. The timing of any repeat biopsy is individual.

A closer look

A tiny sample.
A different level of detail.

SMALL BOWEL
SIMPLIFIED CROSS-SECTION

Small-bowel villi are tiny projections that help provide a surface for absorption. Biopsies let the laboratory assess their architecture and other tissue changes.

Preserved villous architectureShortened or flattened villi
can occur in coeliac disease
Small-bowel lining, simplified cross-sectionPreserved villi are projections of mucosal tissue, covered by epithelium. Crypts dip between them and open into the lumen. The comparison reveals an example with shortened villi while keeping the mucosal support layer. Deeper wall layers and individual cell microvilli are omitted. Optional markers identify one villus tip, a crypt, or a short part of the epithelial surface in each separate tissue example. These markers are not measurements. This is not a histology slide, measurement or diagnosis.
Villi project into the lumenCrypts dip into the mucosa

Select a feature to identify it in the tissue illustration. The tissue stays stationary.

Two illustrative tissue patterns. This is not a severity scale or a change over time.

What the illustration shows

Villi are tissue projections in the small bowel. The epithelial surface continues down into crypts between them. Individual cell microvilli and deeper bowel-wall layers are not shown. The normal colon does not have villi.

Villous changes are interpreted with other biopsy findings, blood tests and clinical history. Villous atrophy alone does not establish coeliac disease. A biopsy may also be useful when the camera view looks normal.

The surface highlight is an optional visual guide. The tissue is stationary. These are simplified examples, not a real biopsy image or a prediction of recovery.

Original schematic, not to scale. Clinical sources: bpacnz and NIDDK.

Information to share with your patient

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References

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