⚠ Important Before You Start Testing
Coeliac antibody tests are only accurate if you are currently eating gluten every day. If you have already started a gluten-free diet, antibody levels fall and results will be falsely negative. Do not start a gluten-free diet before your tests unless specifically advised by your doctor. If you have already removed gluten, inform your consultant — HLA genetic testing can still rule out coeliac disease, and a supervised gluten challenge may be needed.
Contents
Three Different Gluten-Related Conditions
“Gluten intolerance” is a broad term used by patients to describe a range of adverse reactions to gluten. Clinically, there are three distinct conditions with different mechanisms, different tests, and different implications — and it is important to identify which one you have, or whether your symptoms have another cause altogether.
| Condition | Mechanism | Diagnosis | Implications |
|---|---|---|---|
| Coeliac Disease | Autoimmune — T-cell mediated intestinal inflammation triggered by gluten in genetically susceptible individuals (HLA-DQ2/DQ8). Causes villous atrophy in the small intestine. | Serology (tTG IgA, EMA) + intestinal biopsy (gold standard). HLA typing for exclusion. | Strict lifelong gluten-free diet essential. Risk of malnutrition, osteoporosis, anaemia, intestinal lymphoma if untreated. Biopsy confirmation before diet change. |
| Non-Coeliac Gluten Sensitivity (NCGS) | Not fully understood. Not autoimmune, not IgE-mediated. May involve innate immune activation or FODMAPs (fermentable oligosaccharides in wheat). No villous atrophy. | Diagnosis of exclusion — must first rule out coeliac disease and wheat allergy. Symptomatic improvement on GFD with recurrence on gluten challenge. | Gluten-free diet improves symptoms but strict elimination less critical than in coeliac disease. No risk of intestinal damage or malignancy. |
| Wheat Allergy | IgE-mediated allergic reaction to wheat proteins (not specifically gluten). Can cause immediate allergic reactions including anaphylaxis. | Specific IgE to wheat, omega-5-gliadin (Tri a 19), skin prick test. Supervised food challenge for confirmation. | Wheat avoidance (not necessarily all gluten-containing grains). Adrenaline auto-injector if anaphylaxis risk. Other grains (barley, rye) may be tolerated. |
Why this distinction matters: A patient who avoids gluten because they “feel better” without a formal diagnosis may have coeliac disease going undetected and untreated — with ongoing risk of serious complications even on a “mostly gluten-free” diet. Equally, a patient labelled as having coeliac disease without proper testing may be on an unnecessarily strict diet for a condition they do not have. Accurate diagnosis before dietary change is essential.
Coeliac Disease — What You Need to Know
Coeliac disease is a chronic autoimmune condition in which gluten — a protein complex found in wheat, barley, and rye — triggers an abnormal immune response in genetically susceptible individuals. This leads to inflammation and progressive damage to the villi of the small intestine (villous atrophy), impairing nutrient absorption and causing a wide range of symptoms.
Coeliac disease affects approximately 1 in 100 people in the UK, making it one of the most common autoimmune conditions. However, it is estimated that only around 30% of cases in the UK are diagnosed — meaning the majority of people with coeliac disease remain unidentified. The condition can develop at any age, including in adulthood after years of tolerating gluten without obvious symptoms.
Genetics
Almost all people with coeliac disease carry the HLA-DQ2 (approximately 90–95%) or HLA-DQ8 (5–10%) genetic variants. A negative result for both genes makes coeliac disease very unlikely — negative predictive value exceeding 99%. However, approximately 25–30% of the general population carry these genes without ever developing coeliac disease, so HLA positivity alone does not diagnose the condition.
Associated Conditions
- Type 1 diabetes (10-fold increased risk)
- Autoimmune thyroid disease (Hashimoto’s, Graves’)
- IgA deficiency (2–3% of coeliac patients)
- Down’s syndrome, Turner syndrome, Williams syndrome
- First-degree relatives of coeliac patients (10% risk)
Complications of Untreated Coeliac Disease
- Malabsorption: iron, folate, B12, calcium, vitamin D deficiency
- Osteoporosis and fracture risk
- Anaemia
- Infertility and adverse pregnancy outcomes
- Dermatitis herpetiformis (see below)
- Rare: enteropathy-associated T-cell lymphoma (EATL)
Non-Coeliac Gluten Sensitivity (NCGS)
Non-coeliac gluten sensitivity is a clinical syndrome characterised by intestinal and extra-intestinal symptoms that occur on gluten ingestion and resolve on a gluten-free diet, in people in whom coeliac disease and wheat allergy have been excluded. Unlike coeliac disease, NCGS does not cause intestinal villous atrophy or produce coeliac-specific antibodies.
The mechanism of NCGS remains debated. Some evidence suggests the symptoms attributed to “gluten” in NCGS may actually be driven by FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) present in wheat, rather than gluten proteins themselves. This has important practical implications — some patients labelled with NCGS may benefit from a low-FODMAP diet rather than strict gluten elimination.
NCGS is a diagnosis of exclusion. It can only be confirmed after coeliac disease and wheat allergy have been formally ruled out through appropriate testing — while the patient is still consuming gluten. It should not be self-diagnosed or assumed because symptoms improve on a gluten-free diet alone, as many conditions improve coincidentally during dietary change.
Wheat Allergy
Wheat allergy is an IgE-mediated allergic reaction to proteins in wheat. It is distinct from coeliac disease and NCGS — the immune mechanism is entirely different. Wheat allergy can cause immediate allergic reactions — from mild oral tingling to severe anaphylaxis — typically within minutes to two hours of eating wheat.
Wheat-Dependent Exercise-Induced Anaphylaxis (WDEIA)
A specific form of wheat allergy triggered only when wheat ingestion is combined with physical exercise within a few hours. The key allergen is omega-5-gliadin (Tri a 19). WDEIA can cause severe anaphylaxis and is often misdiagnosed. Testing for Tri a 19-specific IgE is essential where this pattern is suspected.
Important Difference from Coeliac Disease
In wheat allergy, only wheat needs to be avoided — barley and rye are usually tolerated (unless there is cross-sensitisation). In coeliac disease, all gluten-containing grains (wheat, barley, rye) must be strictly avoided lifelong. Getting the correct diagnosis therefore has practical dietary consequences.
Occupational Wheat Allergy
“Baker’s asthma” and “baker’s rhinitis” are occupational forms of wheat allergy caused by inhalation of wheat flour dust. Common in bakers, millers, and food industry workers. Diagnosed with specific IgE to wheat and skin prick testing. Occupational health and spirometry assessment may also be required.
Symptoms — What to Look Out For
Coeliac disease and gluten-related conditions produce a wide range of symptoms, many of which are shared with other common conditions — making diagnosis without testing unreliable. Symptoms may be absent, subtle, or atypical, particularly in adults.
Digestive Symptoms
- Bloating and abdominal distension
- Diarrhoea (often pale, fatty, foul-smelling stools)
- Abdominal pain and cramping
- Constipation (in some patients)
- Nausea and vomiting
- Mouth ulcers (aphthous ulceration)
General & Systemic
- Fatigue and low energy
- Unexplained weight loss
- Anaemia (iron deficiency, B12, or folate)
- Delayed growth or puberty (children)
- Joint pain
- Neurological symptoms: headaches, “brain fog”, peripheral neuropathy
Silent / Atypical
- No digestive symptoms at all
- Osteoporosis at a young age
- Recurrent miscarriage or infertility
- Unexplained abnormal liver function tests
- Short stature
- Skin rash (dermatitis herpetiformis — see below)
Wheat Allergy Symptoms
- Immediate: urticaria (hives), angioedema
- Rhinitis, asthma, or wheezing after wheat
- Nausea and vomiting within minutes to 2 hours
- Anaphylaxis (WDEIA: only with exercise)
- Occupational: rhinitis/asthma from flour inhalation
NICE Guideline NG20 recommends offering coeliac testing to anyone with: persistent unexplained gastrointestinal symptoms, first-degree relatives of a person with coeliac disease, type 1 diabetes, autoimmune thyroid disease, IBS-type symptoms (coeliac disease affects up to 5% of IBS diagnoses), unexplained anaemia, fatigue, or bone pain, and in children with faltering growth or delayed puberty.
Testing Available at Our Clinic
We offer a comprehensive range of validated tests for gluten-related conditions, interpreted by an allergy consultant in the context of your full clinical history. All tests must be performed while you are eating gluten regularly (except HLA genetic testing).
Small Intestinal Biopsy — Gold Standard for Coeliac Disease
The gold standard for confirming coeliac disease remains duodenal biopsy at upper endoscopy (gastroscopy), showing villous atrophy (Marsh grade 3 or above). NICE NG20 updated in 2020 allows a biopsy-free diagnosis in children with tTG IgA ≠10 times the upper limit of normal, positive EMA, and positive HLA-DQ2/8, with a compatible clinical picture. For most adults, biopsy is still required for confirmation. We arrange gastroenterology referral for biopsy where clinically indicated.
HLA-DQ2 / HLA-DQ8 Genetic Testing
HLA genetic testing for the DQ2 (DQA1*05 + DQB1*02) and DQ8 (DQA1*03 + DQB1*03:02) alleles is the most clinically useful test when coeliac antibodies cannot be reliably interpreted — particularly when the patient is already following a gluten-free diet.
Negative Result — Very Reassuring
A negative result for both HLA-DQ2 and HLA-DQ8 makes coeliac disease extremely unlikely (negative predictive value >99%). This means you can be reassured that coeliac disease is not the cause of your symptoms, regardless of dietary status. No further coeliac testing or gluten challenge is required.
Positive Result — Does Not Confirm Coeliac Disease
A positive HLA-DQ2/DQ8 result only confirms genetic susceptibility — approximately 25–30% of the general population carries these genes, but only 1% develop coeliac disease. A positive result means coeliac disease remains possible and further testing (antibodies on gluten-containing diet, and/or biopsy) is needed to confirm or exclude the diagnosis.
When HLA Testing Is Most Useful
- Already on a gluten-free diet — antibodies unreliable
- Inconclusive serology — low-positive tTG IgA
- Strong family history — first-degree relative has coeliac disease
- Associated autoimmune conditions (type 1 diabetes, thyroid disease)
- Patient cannot or will not undergo gluten challenge
Already on a Gluten-Free Diet? — What to Do
A very common clinical problem: patients who have removed gluten from their diet because they felt better, and now wish to know whether they have coeliac disease. Once on a strict gluten-free diet, antibody levels fall — sometimes to within normal range within weeks – and a standard blood test will be falsely negative.
Step 1: HLA Genetic Testing First
Request HLA-DQ2/DQ8 testing immediately. This can be done at any time regardless of diet. If the result is negative for both, coeliac disease is effectively excluded and no further testing or gluten challenge is necessary.
Step 2: If HLA Positive — Consider a Gluten Challenge
If HLA-DQ2 or DQ8 is positive, coeliac disease remains possible. A supervised gluten challenge is needed to enable accurate antibody and biopsy testing. The standard protocol recommended by BSG/NICE is ingestion of at least 3–10 g of gluten daily (equivalent to approximately 2–4 slices of wheat bread) for a minimum of 6 weeks before repeat serology. Symptoms during challenge should be monitored with consultant support.
Step 3: Repeat Serology and Biopsy if Indicated
After the 6-week gluten challenge, repeat tTG IgA, EMA, and total IgA. If serology is positive, gastroenterology referral for duodenal biopsy confirms the diagnosis. If symptoms during challenge are severely debilitating, discuss with your consultant — the challenge period can be shortened but at the cost of reduced test sensitivity.
Dermatitis Herpetiformis (DH)
Dermatitis herpetiformis is a specific skin manifestation of coeliac disease — it is not a separate condition but rather the cutaneous expression of the same autoimmune process. It presents as an intensely itchy, blistering rash typically affecting the elbows, knees, buttocks, back, and scalp. It is more common in men than women and often presents without any gastrointestinal symptoms.
Diagnosis
Skin biopsy of perilesional skin showing granular IgA deposits at the dermo-epidermal junction (direct immunofluorescence) is diagnostic. Serology (tTG IgA, EMA, anti-DGP IgA) is usually positive. HLA-DQ2/DQ8 carries the same genetic association as intestinal coeliac disease.
Treatment
A strict lifelong gluten-free diet is the primary and most important treatment — both for the skin and to protect against intestinal complications and lymphoma risk. Dapsone (an antibiotic with anti-inflammatory properties) rapidly controls skin symptoms but does not address the underlying gluten-triggered autoimmune process.
Shared Care
Patients with DH are managed jointly by allergy/immunology (for serological monitoring and dietary guidance) and dermatology (for skin biopsy and topical/systemic treatment). Our clinic offers both dermatology and allergy/immunology consultants.
Where Gluten Is Found
✗ Contains Gluten — Avoid in Coeliac Disease
- Wheat and all its varieties: spelt, khorasan (Kamut), emmer, einkorn, durum, semolina, triticale
- Barley (including malt, malt extract, malt vinegar, malt whisky)
- Rye
- Products made from these: bread, pasta, pizza bases, cakes, biscuits, pastry, crackers, most breakfast cereals, many ready meals, soups, sauces, and processed foods
✓ Naturally Gluten-Free
- Rice, maize (corn), potatoes, polenta
- Quinoa, buckwheat, millet, sorghum, teff, amaranth
- Plain meat, fish, eggs, cheese, milk, fruit, vegetables, pulses
- Gluten-free oats (see below)
◆ Oats — Requires Caution
Oats contain avenin, which is structurally distinct from gluten. The majority of people with coeliac disease tolerate oats, but:
- A small minority (approximately 1–5%) react to avenin itself
- Standard oats are frequently contaminated with wheat, barley, or rye during growing and processing
- Only certified gluten-free oats (tested to <20 ppm gluten) should be used in coeliac disease
- Oats should be introduced only after the intestine has healed on a gluten-free diet, and with monitoring
Hidden gluten: Gluten is found in many unexpected places including soy sauce, beer, malt vinegar, some medications and supplements (excipients), communion wafers, and shared cooking equipment. Under UK Food Information Regulations (retained from EU law), wheat, barley, and rye are listed as mandatory allergens that must be declared on pre-packed food labels in bold. For non-pre-packed foods (e.g. restaurant meals), always ask about allergen content.
Gluten-Free Diet — Key Principles
A gluten-free diet (GFD) is the only treatment for coeliac disease. It must be strict and lifelong. Even small amounts of gluten — as little as a crumb — can trigger mucosal damage in susceptible patients even without obvious symptoms. The principles of a successful GFD include:
Reading Labels
Always read ingredient lists. “Gluten-free” on a UK label means <20 ppm gluten (legally defined). “Very low gluten” means <100 ppm — generally not safe for coeliac disease.
Cross-Contamination
Use separate cooking equipment (toasters, colanders, chopping boards). Do not share butter, jam, or spreads with those who use them with gluten-containing bread. Be vigilant in shared kitchens.
Eating Out
Always inform the restaurant or café of your coeliac diagnosis. Use Coeliac UK’s Gluten-Free On The Move app and cross-grain symbol to identify vetted eateries. A meal described as “gluten-free” on a menu must be prepared with full cross-contamination precautions.
Nutritional Balance
Gluten-free substitute products (breads, pasta) are often lower in fibre, B vitamins, and iron than their wheat equivalents. Focus on naturally gluten-free whole foods. Dietitian input is recommended at diagnosis and at follow-up.
Monitoring
Annual follow-up is recommended including repeat tTG IgA (to assess adherence and mucosal healing), full blood count, iron, ferritin, B12, folate, vitamin D, and bone density (DEXA scan) at diagnosis and periodically. Persistently elevated tTG IgA on a GFD suggests ongoing gluten exposure.
Continuing Symptoms on GFD
If symptoms persist after 3 months on a strict GFD, review possible inadvertent gluten exposure. If excluded, a gastroenterology referral is indicated to assess for complications: refractory coeliac disease, microscopic colitis, or other gastrointestinal conditions.
Family Screening
First-degree relatives (parents, children, siblings) of a person with confirmed coeliac disease have approximately a 1 in 10 chance of also having coeliac disease, compared with 1 in 100 in the general population. NICE NG20 and Coeliac UK recommend testing all first-degree relatives, even if they have no symptoms.
Screening should include tTG IgA and total IgA while the relative is eating a normal gluten-containing diet. HLA typing can be used to exclude susceptibility in those who prefer to avoid serology or gluten challenge. Children of a parent with coeliac disease should be tested — ideally from age 3 and repeated if new symptoms develop, as coeliac disease can appear at any age.
Frequently Asked Questions
Trusted UK Resources
Coeliac UK — What Is Coeliac Disease? →
coeliac.org.uk — leading UK charity for coeliac disease, gluten-free diet support
NICE Guideline NG20 — Coeliac Disease →
NICE guideline on recognition, assessment, and management of coeliac disease
BSG Guidelines — Coeliac Disease →
British Society of Gastroenterology clinical guidelines for coeliac disease
Information on lactose intolerance testing at our clinic
Wheat Allergy Molecular Testing (ALEX³) →
ALEX³ includes wheat-specific IgE and Tri a 19 (omega-5-gliadin) in its 300-allergen panel
Important Notice
This page provides general educational information only and is not a substitute for individual medical advice. Do not start a gluten-free diet before testing without discussing with your doctor. All diagnoses are made by qualified consultants following full clinical assessment. In a medical emergency, call 999.
References
- NICE. Coeliac Disease: Recognition, Assessment and Management. NG20. July 2015; updated October 2020. nice.org.uk/guidance/ng20
- Ludvigsson JF, Bai JC, Biagi F, et al. Diagnosis and management of adult coeliac disease: guidelines from the British Society of Gastroenterology. Gut. 2014;63:1210–1228. Updated BSG guidance 2022.
- Husby S, Koletzko S, Korponay-Szabó I, et al. European Society Paediatric Gastroenterology, Hepatology and Nutrition guidelines for diagnosing coeliac disease 2020. J Pediatr Gastroenterol Nutr. 2020;70(1):141–156.
- Catassi C, Elli L, Bonaz B, et al. Diagnosis of Non-Celiac Gluten Sensitivity (NCGS): The Salerno Experts’ Criteria. Nutrients. 2015;7(6):4966–4977.
- Hemmings O, et al. Ara h 2 is the dominant peanut allergen despite similarities with Ara h 6. J Allergy Clin Immunol. 2020 [reference for wheat component testing context].
- Coeliac UK. What Is Coeliac Disease? coeliac.org.uk. Accessed June 2026.
Page reviewed: June 2026 | London Allergy and Immunology Centre | privateallergy.uk