Confirm the diagnosis before starting lifelong treatment
I check your gluten intake, antibody results and IgA level before deciding whether you need gastroscopy and duodenal biopsies. The bowel can look normal at gastroscopy despite microscopic coeliac disease. Please keep eating gluten until we have agreed and completed your diagnostic plan.
How New Zealand and overseas diagnostic pathways differ
The practical New Zealand starting point is a blood test while you are eating gluten, followed by an agreed diagnostic assessment. A positive result should not simply become a label in your record without confirmation. I check your actual antibody result, the laboratory limit, gluten intake and whether there is another reason for gastroscopy.
Overseas adult guidelines now allow selected people with very high antibodies to be diagnosed without biopsies, but their criteria differ. That does not establish an automatic New Zealand pathway. I would discuss whether this option is suitable with you and the relevant service. Children have a separate diagnostic pathway.
Understand the test before changing your diet
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.
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.
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.
What happens in the small bowel?
Gluten is found in wheat, barley and rye. In coeliac disease it triggers an immune response that can damage the villi, the tiny projections that help absorb nutrients. The change varies between people and can be patchy. The appearance of the villi does not tell me exactly how unwell you feel.
This is different from wheat allergy or symptoms associated with wheat in someone without coeliac disease. Feeling better without bread does not distinguish these conditions, because changing wheat intake also changes other parts of the diet.
Coeliac disease can occur without diarrhoea
Coeliac disease can cause diarrhoea, bloating, constipation, tiredness, weight loss or mouth ulcers. Sometimes the first clue is iron deficiency, low bone density or another nutritional problem.
Some people have few obvious symptoms. I look at your symptoms alongside blood tests, family history and any nutritional problems. No single bowel symptom confirms or rules out coeliac disease.
A parent, brother, sister or child of someone with confirmed coeliac disease should discuss testing with their GP, even if well. Type 1 diabetes and some other autoimmune conditions also increase the chance.
What does the blood test show?
The usual first tests are IgA tissue transglutaminase antibodies (tTG-IgA) and total IgA. Total IgA checks whether you make enough of this antibody type for the result to be interpreted. If IgA is low, the laboratory or clinician may use an appropriate IgG-based test.
A negative result is less reliable if you have already reduced gluten. Strong clinical suspicion may still justify specialist assessment despite negative antibodies. A mildly positive result and a very high result are not interpreted in the same way.
Why might I need a gastroscopy and biopsies?
Gastroscopy allows small tissue samples from the duodenum, the first part of the small bowel. The lining can look normal to the camera even when microscopic changes are present. Several samples help assess a condition that may be patchy.
Biopsies remain useful with lower antibody levels, uncertain results, IgA deficiency, concerning symptoms or another reason to examine the upper gut. Your recommended follow-up will be documented in the endoscopy report and/or histology report once tissue results are available.
What if I have already stopped gluten?
Tell me how long you have avoided it and bring previous blood tests and biopsy reports. Do not assume a normal test taken on a gluten-free diet excludes coeliac disease. We may consider gene testing to help exclude it, or agree a supervised gluten challenge before repeating diagnostic tests.
A positive HLA-DQ2 or DQ8 gene test does not diagnose coeliac disease. These genes are common in people who never develop it. If you need to eat gluten again for testing, we will agree how much and for how long. Please get in touch with me if symptoms make this difficult.
Starting a gluten-free diet after diagnosis
Treatment is a strict, lifelong gluten-free diet. A dietitian and Coeliac New Zealand can help with food labels, eating out, travel and avoiding cross-contact. Aim for a varied, balanced diet. Do not keep removing foods unless we have identified a reason.
We also check for deficiencies and consider bone health according to your circumstances. Symptoms often improve before the bowel lining has fully recovered. Feeling well does not make regular gluten exposure safe in confirmed coeliac disease.
What if symptoms or blood tests remain abnormal?
Follow-up considers symptoms, weight, diet, antibodies and any original deficiencies together. Falling antibodies are useful, but normal antibodies do not prove that the lining has healed. Repeat biopsies are considered according to the diagnosis, recovery and remaining concerns.
If you are still unwell, I first review the original diagnosis and possible gluten exposure. Other conditions, including IBS or lactose intolerance, can coexist. Persistent symptoms do not automatically mean refractory coeliac disease. New weight loss, persistent anaemia or worsening pain need reassessment.
A tiny sample.
A different level of detail.
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.
can occur in coeliac disease
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.
When to seek advice
Arrange prompt medical review for unexplained weight loss, persistent vomiting, worsening pain, bleeding or continuing iron deficiency. These changes should not simply be attributed to coeliac disease or gluten exposure.
Severe pain, vomiting blood, black tarry stools with faintness or collapse need urgent assessment. Call 111 if you collapse or are too unwell to travel safely.
Three things to remember
- Keep eating gluten until the diagnostic plan is complete, unless your clinical team advises otherwise.
- A confirmed diagnosis guides lifelong treatment, family testing and follow-up.
- Feeling better does not always mean the bowel has healed. Keep your recommended follow-up appointments and blood tests.
Related information
Sources and further reading
English clinical master checked 16 October 2026.
- bpacnz and Coeliac NZ: primary care checklist (2025)
- Coeliac New Zealand: diagnosis information and local support
- bpacnz: coeliac investigation and management (2022)
- ESsCD: adult diagnostic guideline (2025)
- BSG: adult coeliac guideline (2026)
- NIDDK: diagnosing coeliac disease
- NIDDK: treatment and follow-up