Coeliac disease blood test: why not to cut gluten first

If you suspect gluten is making you ill, it is tempting to cut it out straight away and see what happens. With coeliac disease, that is the one thing official UK guidance asks you not to do before you have been tested. This guide explains how diagnosis works in the UK, step by step, and why timing your gluten matters so much.

The key point

Keep eating gluten until testing is complete. NICE advises eating some gluten in more than one meal every day for at least six weeks before testing, and not starting a gluten-free diet until a specialist confirms the diagnosis, even if your blood test is positive (NICE NG20, 1.1.3–1.1.4).

Who should be tested?

The NHS says you should be tested if you have any one of a list of symptoms or conditions, including persistent unexplained gut symptoms (such as diarrhoea, stomach ache and bloating), prolonged tiredness, unintentional weight loss, severe or persistent mouth ulcers, unexplained iron, vitamin B12 or folate deficiency anaemia, type 1 diabetes, autoimmune thyroid disease, or irritable bowel syndrome (IBS) in adults. Testing is also recommended if a parent, brother, sister or child has coeliac disease.

NICE recommendation 1.1.2 adds a second list of situations where testing should be considered, such as reduced bone density, unexplained neurological symptoms, unexplained subfertility or recurrent miscarriage, persistently raised liver enzymes, dental enamel defects, Down’s syndrome and Turner syndrome.

For an overview of symptoms and the condition itself, see what is coeliac disease?

Why you must keep eating gluten

The blood test looks for antibodies your body makes in response to eating gluten. Coeliac UK explains that removing or reducing gluten before testing will affect your results, and can lead to a false negative. NICE also warns that if you have already cut gluten out, it may be difficult to confirm the diagnosis by biopsy.

That is why the NHS says you need to eat foods containing gluten while being tested, and should not start a gluten-free diet until a specialist confirms the diagnosis.

How much gluten is enough?

NICE: some gluten in more than one meal every day for at least six weeks before testing (recommendation 1.1.4).
Coeliac UK: at least 3 g, and preferably 6 g, of gluten a day for at least six weeks before testing and throughout the diagnosis process. Its getting diagnosed page gives examples of portions containing about 3 g of gluten, such as around 1.5 to 2 slices of wheat bread or a fist-sized portion of cooked wheat pasta.

If you’ve already cut out gluten

This is very common, and it’s not a reason to avoid your GP. Reintroducing gluten before testing is called a gluten challenge. Coeliac UK advises discussing it with your GP first, because it can bring symptoms back, and your GP can arrange testing at the right time.

If you can’t or don’t want to reintroduce gluten, NICE recommendation 1.1.5 says you should be referred to a gastrointestinal specialist, and that it may be difficult to confirm the diagnosis by biopsy. NICE also allows HLA genetic testing in specialist settings for some people who already have limited gluten intake and choose not to have a gluten challenge (1.2.6). NICE says genetic testing should not be used for initial diagnosis in non-specialist settings (1.2.5).

Step 1: the blood test

Your GP arranges a blood test. NICE recommends that laboratories test for:

total immunoglobulin A (IgA), to check you make IgA antibodies normally; and
IgA tissue transglutaminase antibodies (tTG), the main coeliac antibody test.

If the tTG result is only weakly positive in a young person or adult, the lab should use a second antibody test, IgA endomysial antibodies (EMA). Some people are IgA deficient, meaning the usual tests can miss coeliac disease; for them, IgG-based tests (IgG EMA, IgG DGP or IgG tTG) should be considered (NICE 1.2.2; Coeliac UK).

What if the result is negative?

The NHS notes that it is possible to have coeliac disease without these antibodies in your blood, and a GP may still refer you to a specialist if symptoms continue. NICE says people with negative results should be referred for further assessment if coeliac disease is still suspected (1.3.3). If you weren’t eating enough gluten before the test, tell your GP, as that can cause a false negative.

Step 2: seeing a specialist

If the antibodies are found, your GP refers you to a gastroenterologist (gut specialist), or a paediatric specialist for children (NICE 1.3.1–1.3.2). Keep eating gluten while you wait.

The biopsy (endoscopy)

For many adults, the diagnosis is confirmed by a biopsy of the small intestine. The NHS explains that a thin, flexible tube with a camera (an endoscope) is passed through your mouth into your small intestine, usually after a local anaesthetic throat spray and sometimes a sedative. Tiny samples of the gut lining are taken and examined under a microscope.

The no-biopsy route for some adults (new in 2026)

In July 2026 the British Society of Gastroenterology (BSG) published updated guidelines for adult coeliac disease. They suggest that symptomatic adults being assessed in secondary care (by a hospital specialist, not in general practice) can be diagnosed without a biopsy if their IgA-tTG level is at least 10 times the upper limit of normal.

The guideline is clear that this route is optional and should only be used after shared decision-making with the patient. Endoscopy is still important for people with “red flag” symptoms or where another condition is suspected. Coeliac UK’s summary estimates that around 20 to 30% of symptomatic adults may have antibody levels high enough to qualify.

Children have been diagnosed without a biopsy in some cases for longer. Your child’s specialist will explain the options, which NICE says may include an EMA test, genetic testing or a biopsy (1.3.2).

Questions you could ask your specialist

Do I need a biopsy, or am I eligible for diagnosis from the blood test alone?
Should I keep eating gluten until a particular date or appointment?
When will I be referred to a dietitian?
Which follow-up tests (such as blood tests or a bone density scan) do I need?

Home test kits

Finger-prick coeliac tests are sold in pharmacies and online. Coeliac UK says they do not provide an accurate medical diagnosis and are not recognised by national medical guidelines. Whatever the result, talk to your GP. Coeliac UK also lists tests that are not used to diagnose coeliac disease, including hair analysis, IgG food antibody “intolerance” tests, applied kinesiology and Vega testing.

After diagnosis

Once a specialist confirms coeliac disease, the treatment is a strict, lifelong gluten-free diet. The NHS says you may have further blood tests to check iron and vitamin levels, a skin biopsy if dermatitis herpetiformis is suspected, and possibly a DEXA scan to check bone density. NICE recommends an annual review (1.4.3).

When you are ready to start, these guides will help:

Frequently asked questions

Should I go gluten-free before my coeliac blood test?

No. The NHS and NICE both say you need to keep eating gluten while you are being tested, because the tests are only accurate if gluten is in your diet. NICE advises eating some gluten in more than one meal every day for at least six weeks before testing.

What blood test is used for coeliac disease?

NICE recommends that laboratories test total immunoglobulin A (IgA) and IgA tissue transglutaminase antibodies (tTG) as the first choice, with IgA endomysial antibodies (EMA) if the tTG result is weakly positive, and IgG-based tests for people who are IgA deficient.

Can I be diagnosed without a biopsy?

Sometimes. The 2026 British Society of Gastroenterology guideline suggests that symptomatic adults assessed by a specialist in secondary care can be diagnosed without a biopsy if their IgA-tTG level is at least 10 times the upper limit of normal. It is optional and should be a shared decision with your specialist. Some children can also be diagnosed without a biopsy.

Are home coeliac test kits reliable?

Coeliac UK says home testing kits do not give a confirmed medical diagnosis and are not recognised by national medical guidelines. Whatever the result, discuss your symptoms with your GP.

Can I have coeliac disease with a negative blood test?

Yes, it is possible. The NHS says some people with coeliac disease do not have the antibodies in their blood, and that a GP may still refer you to a specialist if symptoms continue. Not eating enough gluten before the test is another common reason for a false negative.

Sources

Coeliac disease: diagnosis, NHS. Accessed 4 October 2026.
Coeliac disease: recognition, assessment and management (NG20), recommendations 1.1–1.3, NICE. Accessed 4 October 2026.
When you should be tested for coeliac disease (information for the public), NICE. Accessed 4 October 2026.
Getting diagnosed (including the gluten challenge), Coeliac UK. Accessed 4 October 2026.
Blood tests and biopsy, Coeliac UK. Accessed 4 October 2026.
Home tests, Coeliac UK. Accessed 4 October 2026.
The 2026 British Society of Gastroenterology guidelines on the diagnosis and management of adult coeliac disease (Penny HA et al., Gut), Gut (BMJ). Accessed 4 October 2026.
BSG guideline on the diagnosis and management of adult coeliac disease: the highlights, Coeliac UK. Accessed 4 October 2026.