Diagnosis in adults
Coeliac disease in adults is traditionally diagnosed by serological testing and endoscopic intestinal biopsy, but in response to the Covid-19 pandemic, interim guidelines for a no biopsy diagnosis in adults were published by the British Society of Gastroenterology (BSG). Since then, further research has supported this position, and the revised 2026 BSG guidelines formally recognises some adults may be diagnosed with coeliac disease from a single blood test when assessed by a gastroenterologist and in discussion with the patient.
Serological tests
When requesting tests for adults, BSG and NICE recommends:
- Test for total immunoglobin A (IgA) and IgA tissue transglutaminase (tTG) as a first choice test.
- Consider using IgG tTG, IgG endomysial antibodies (EMA), or IgG deamidated gliadin peptide (DGP) in cases of IgA deficiency.
Adults with a positive blood test and those with negative antibodies but where coeliac disease is suspected should be referred to a gastroenterologist, even if they may be eligible for a no biopsy diagnosis.
When can a no biopsy pathway be considered in adults?
The latest BSG guidelines recommend:
- Symptomatic adults being assessed in secondary care settings
- IgA tTG is ≥10 times the upper limit of normal (ULN) for the assay
- No other reasons to have an endoscopy
- Pathway is optional and should be adopted only after shared decision making with the patient
- Laboratories using the 10xULN threshold should participate in external tTG quality assurance for example UK-NEQAS or a local audit to confirm accuracy and applicability of assay.
Endoscopy and biopsy
The majority of adults will still require an endoscopy and biopsy to confirm the diagnosis of coeliac disease. For example, patients with red flag symptoms, other risk factors that require an endoscopy or recently diagnosed with another autoimmune condition.
BSG and NICE recommends an endoscopy and biopsy should be performed within 6 weeks of referral to specialist services.
The BSG advises taking at least 2 biopsies from the duodenum bulb (D1) and 4 biopsies from the second part of the duodenum (D2) and place samples in separate pathology pots to help histological interpretation.
IgA deficiency
Total IgA should be measured when testing for coeliac disease because IgA deficiency is more common in people with coeliac disease than the general population. People with IgA deficiency will have a false negative serological result when tested for IgA antibody, which may lead to a missed diagnosis of coeliac disease.
For adults with IgA deficiency, the no biopsy pathway should not be offered. An endoscopy and biopsy should be performed alongside IgG-based coeliac serology to confirm or exclude coeliac disease.
Potential coeliac disease
A diagnosis of potential coeliac disease can be made in patients with persistently positive antibody test, HLA genes associated with coeliac disease but normal or minimal changes on duodenal biopsies.
The BSG recommends trialling the gluten free diet for these symptomatic patients with the support of a specialist dietitian. If there is no clinical improvement on the gluten free diet, an alternative cause for symptoms should be explored.
People with potential coeliac disease should receive the same follow up as people diagnosed with coeliac disease. If someone with potential coeliac disease continues eating gluten, the BSG advises discussing with the patient about the need to repeat serology and biopsies 1-2 years after diagnosis or if new symptoms develop.
Seronegative coeliac disease
Seronegtaive coeliac disease can be diagnosed when coeliac serology is negative but villous atrophy is present with compatible HLA genetics and patient demonstrates improvement on a gluten free diet.
You can read more about seronegative coeliac disease here.
Ultra short coeliac disease
Ultra short coeliac disease (USCD) refers to patients with positive coeliac serology, but villous atrophy is only present within the first part of the duodenum (D1). Research suggests USCD accounts for 8% of adults with coeliac disease. If a patient has histological changes only in D1 but coeliac disease serology is negative, alternative diagnosis should be considered.
Clinical response to a gluten free diet is similar to conventional coeliac disease and patients should receive the same follow up care as conventional coeliac disease.
Advice before testing
It is important to inform people undergoing testing for coeliac disease that to get accurate test results, they should continue to eat a gluten containing diet before and during the diagnosis process.
BSG recommends 3-6g of gluten every day for at least six weeks before testing. The table below provides examples of food portions that contain 3g of gluten that can be used for a gluten challenge.
| Gluten containing food | 3g of gluten |
| Sourdough spelt bread | 60g (1.5 – 2 slices bread / medium bread roll) |
| Wheat-based breakfast cereal e.g. Shredded wheat/ Weetabix | 25g wheat-based cereal such as two Weetabix or two fist-sized portions of cereal |
| Wheat-based bread | 60g (1.5 – 2 slices bread / medium bread roll) |
| Wheat-based cooked pasta | 90g of cooked pasta (a fist-size portion) |
| Wheat-based biscuits | 50g (3-5 biscuits) |
| Wheat gluten flour or vital wheat gluten | 7.5g (1.5-2 teaspoons) |
A gluten free diet should not be initiated until diagnosis is confirmed by a specialist, even if the results of a serological test are positive.
If people have already restricted their gluten intake or excluded gluten from their diet are unable to reintroduce gluten into their diet before testing, refer the patient to a gastroenterologist and explain that it may be difficult to confirm their diagnosis.