Coeliac Disease: An Immune Reaction to Gluten

Coeliac disease is a lifelong autoimmune condition triggered by gluten. The immune reaction damages the small bowel lining and can reduce nutrient absorption. Symptoms range from diarrhoea and bloating to anaemia, weak bones, infertility, neurological problems or no noticeable symptoms.

What coeliac disease is Coeliac disease is a lifelong autoimmune condition triggered by eating gluten. Gluten is a group of proteins found in wheat, barley and rye. It is present in many breads, cereals, pastas, baked foods, sauces and processed products. In coeliac disease, gluten activates an abnormal immune response that damages the lining of the small bowel. This damage can interfere with nutrient absorption and produce symptoms throughout the body, not only within the digestive system. Coeliac disease can begin at any age after gluten has been introduced into the diet. Coeliac disease is not an allergy or ordinary intolerance Coeliac disease is an autoimmune disease. It is not a food allergy and is not simply an inability to digest gluten. The immune reaction in coeliac disease targets the small bowel lining and can cause persistent tissue damage even when symptoms are mild or absent. A wheat allergy is a different immune reaction to one or more wheat proteins. It can cause hives, swelling, wheezing, vomiting or anaphylaxis, often soon after exposure. Non coeliac gluten sensitivity is another distinct label. It describes symptoms associated with gluten containing or wheat containing foods after coeliac disease and wheat allergy have been excluded. These conditions require different investigations and dietary advice. They should not be treated as interchangeable diagnoses. What happens inside the small bowel The small bowel absorbs nutrients after food leaves the stomach. Its inner surface contains millions of tiny finger like projections called villi. Villi create a large surface area for absorbing iron, vitamins, minerals, fats, proteins and carbohydrates. In coeliac disease, immune cells accumulate within the lining. The normal intestinal glands can lengthen, and the villi can become shortened or flattened. Flattening of the villi is called villous atrophy. Reduced absorbing surface can lead to malabsorption, nutritional deficiencies and symptoms beyond the digestive tract. Gluten and the immune reaction Gluten includes proteins such as gliadin in wheat, hordein in barley and secalin in rye. During digestion, gluten produces fragments that interact with tissue transglutaminase within the bowel lining. In genetically susceptible people, immune cells recognise these modified fragments and produce inflammation. Antibodies against tissue transglutaminase and related structures can become detectable in the blood. The biology is more complex than one antibody alone. Coeliac disease requires gluten exposure, genetic susceptibility and an inappropriate immune response. Symptoms vary greatly Coeliac disease has no single universal presentation. Some people develop persistent diarrhoea, abdominal pain, bloating and weight loss. Others have constipation, indigestion, vomiting or only mild intermittent discomfort. Some people have no recognisable bowel symptoms. They may be diagnosed after investigation of anaemia, osteoporosis, neurological symptoms or another associated condition. A person can have significant small bowel damage without feeling severely unwell. The absence of diarrhoea does not exclude coeliac disease. Classic gastrointestinal symptoms Diarrhoea occurs when the damaged bowel cannot absorb nutrients and fluid normally. Stools may become bulky, pale, greasy, frothy, unusually foul smelling or difficult to flush. Fat rich stool is called steatorrhoea. Abdominal bloating, excessive wind and cramping are common but non specific symptoms. Some people experience nausea, vomiting, constipation or recurring indigestion rather than diarrhoea. Similar symptoms occur in irritable bowel syndrome, lactose intolerance, inflammatory bowel disease, infections and several other conditions. Iron deficiency anaemia Iron is mainly absorbed in the upper small bowel, which is commonly affected by coeliac disease. Coeliac disease can therefore present as unexplained or repeatedly recurring iron deficiency anaemia. Possible symptoms include tiredness, reduced exercise tolerance, breathlessness, headaches, palpitations and pale skin. Anaemia may occur without diarrhoea, abdominal pain or weight loss. Persistent anaemia still requires investigation for blood loss and other causes. Coeliac disease should not be assumed from iron deficiency alone. Other vitamin and mineral deficiencies Malabsorption can contribute to folate, vitamin B12, vitamin D, calcium and other nutrient deficiencies. Folate or vitamin B12 deficiency can cause anaemia, fatigue and neurological symptoms. Vitamin D and calcium abnormalities can weaken bone and contribute to osteomalacia or osteoporosis. Reduced food intake and an unnecessarily restrictive diet can worsen deficiency after diagnosis. Blood tests and dietary assessment guide supplementation. Supplements do not replace removal of gluten. Osteoporosis and bone health Coeliac disease can reduce bone mineral density through calcium and vitamin D malabsorption, inflammation and secondary hormonal changes. Some people first come to attention after a low impact fracture or an osteoporosis assessment. Current BSG adult guidance advises a bone density scan around one year after starting the gluten free diet for newly diagnosed adults. The exact approach in children and individual adults depends on age, fractures, nutritional status and other risk factors. Bone health usually improves when gluten is excluded and deficiencies are corrected, although established osteoporosis may require additional treatment. Dermatitis herpetiformis Dermatitis herpetiformis is a strongly gluten associated autoimmune skin condition. It causes intensely itchy groups of small blisters or raised spots. Common sites include the elbows, knees, buttocks, scalp and back. Scratching may remove the blisters before they are examined, leaving crusts, marks or excoriations. A specialist may confirm the condition using a skin biopsy taken beside an active lesion. The long term treatment is the same lifelong gluten free diet used for intestinal coeliac disease. Dapsone may control the rash while the diet begins working. It requires specialist prescribing and blood monitoring because it can cause serious adverse effects. Fertility and pregnancy related presentations Untreated coeliac disease is associated with unexplained subfertility and recurrent miscarriage in some people. Nutritional deficiencies and active inflammation may contribute, although fertility problems have many other causes. Poorly controlled coeliac disease during pregnancy has been associated with low birth weight and other pregnancy complications. A strict gluten free diet and correction of deficiencies support reproductive and pregnancy health. Coeliac disease does not mean that a person cannot become pregnant or have a healthy pregnancy. Neurological presentations Coeliac disease can be associated with tingling, numbness, altered sensation or peripheral neuropathy. Some people develop problems with balance, coordination or speech called gluten ataxia. Headaches, fatigue and cognitive difficulties are also reported but have many possible explanations. Neurological symptoms may persist despite limited digestive symptoms. New weakness, sudden loss of coordination, speech difficulty or other acute neurological changes require emergency assessment for common neurological emergencies. Mouth, teeth and liver findings Severe or repeatedly recurring mouth ulcers can be associated with coeliac disease. Children and adults may develop defects in dental enamel, although these have other possible causes. Some people have persistently raised liver enzymes that improve after diagnosis and dietary treatment. Abnormal liver tests still require assessment for fatty liver disease, viral hepatitis, alcohol related disease, medicines and other liver conditions. Children and young people Children may develop diarrhoea, abdominal swelling, vomiting, irritability or constipation. Malabsorption can cause faltering growth, low weight, delayed puberty, anaemia or reduced bone strength. Some children mainly show tiredness, mouth ulcers, poor appetite or changes in school performance. Growth should be assessed using height and weight over time rather than one measurement alone. Testing should not be performed before gluten has been introduced into the child's diet. Children with positive tests require assessment through an appropriate paediatric specialist pathway. Coeliac disease can be asymptomatic Some people have no symptoms they recognise as abnormal. They may be tested because a close relative has coeliac disease or because they have type 1 diabetes, autoimmune thyroid disease or another associated condition. Biopsy changes and nutrient deficiencies can still be present in an asymptomatic person. Treatment is recommended after a secure diagnosis because ongoing gluten exposure can produce complications even without obvious symptoms. Asymptomatic disease should not be confused with a false positive antibody result. Specialist confirmation remains important. Conditions associated with coeliac disease Coeliac disease is more common in first degree relatives of affected people. Testing is also recommended or considered in several higher risk groups. These include people with type 1 diabetes, autoimmune thyroid disease, Down syndrome or Turner syndrome. Coeliac disease can coexist with autoimmune liver disease, selective IgA deficiency and other immune mediated conditions. An associated condition increases suspicion but does not confirm coeliac disease. Why testing must happen while eating gluten Coeliac blood tests and bowel biopsies detect the immune and tissue changes produced by eating gluten. Removing gluten can lower antibody levels and allow the bowel lining to heal. Starting a gluten free diet before testing can therefore create false negative blood or biopsy results. NICE advises people on a normal diet to eat some gluten in more than one meal every day for at least six weeks before testing. The 2026 BSG adult guideline recommends 3 to 6 grams of gluten daily for at least six weeks when a formal gluten challenge is needed. Do not begin a gluten challenge independently if eating wheat has previously caused breathing difficulty, throat swelling, collapse or another possible allergic reaction. Do not start a gluten free diet before diagnosis A person may understandably want to test whether avoiding gluten improves symptoms. However, symptom improvement does not confirm coeliac disease. Removing wheat can also reduce fermentable carbohydrates or other food components that cause symptoms. Once gluten has been removed, reintroducing enough for reliable testing may be difficult or unpleasant. Continue the usual gluten containing diet until the diagnostic process is complete unless a specialist advises otherwise. People already avoiding gluten should be referred for specialist discussion rather than assuming that ordinary tests will remain accurate. The first blood tests The first line blood test in young people and adults is IgA tissue transglutaminase antibody, usually called IgA tTG or tTG IgA. Total immunoglobulin A should be checked alongside it because selective IgA deficiency can make an IgA based test falsely negative. If tTG IgA is weakly positive, an IgA endomysial antibody test may help clarify the result. If the person is IgA deficient, laboratories can use IgG based tests such as IgG tTG, IgG endomysial antibody or IgG deamidated gliadin peptide. Blood results must be interpreted using the laboratory's reference range and the amount of gluten being eaten. A positive tTG result is not the whole diagnosis tTG IgA is sensitive and useful, but it is not perfect. False positive or borderline results can occur, including with some autoimmune and liver conditions. False negative results can occur with IgA deficiency, limited gluten exposure, mild disease or seronegative coeliac disease. A strongly positive result makes coeliac disease more likely but still requires specialist review. Do not diagnose or exclude coeliac disease from a home test or one antibody value without clinical interpretation. Duodenal biopsy For most adults, diagnosis is confirmed through upper gastrointestinal endoscopy with duodenal biopsies. A flexible camera passes through the mouth and stomach into the first part of the small bowel. Sedation or throat spray may be offered. Several small tissue samples are collected from the duodenal bulb and the second part of the duodenum. Multiple samples matter because inflammation can be uneven and may be missed by inadequate sampling. The person must remain on a gluten containing diet until the biopsies have been completed. What the biopsy can show A pathologist examines the number of immune cells, the depth of intestinal glands and the shape of the villi. Characteristic findings include increased intraepithelial lymphocytes, crypt hyperplasia and shortening or flattening of villi. Complete villous atrophy is a classic feature but is not required in every confirmed case under current adult guidance. Similar biopsy abnormalities can occur with infections, medicines, immune deficiencies and other intestinal diseases. Biopsy findings therefore require interpretation alongside serology, gluten exposure and the wider clinical picture. A selected no biopsy pathway for adults Current NICE guidance retains specialist endoscopic biopsy as the usual confirmation pathway for adults with positive serology. The 2026 BSG guideline introduces an optional no biopsy pathway for selected symptomatic adults assessed in secondary care. This pathway may be considered when tTG IgA is at least ten times the assay's upper limit of normal and other conditions are satisfied. It requires specialist oversight and shared decision making. It is not a shortcut for self diagnosis or a positive test managed only in primary care. Biopsy remains appropriate when results are less strongly positive, symptoms are atypical, another diagnosis requires endoscopy or tests disagree. HLA DQ2 and HLA DQ8 testing Most people with coeliac disease carry HLA DQ2 or HLA DQ8 genetic variants. However, these variants are common in people who never develop coeliac disease. A positive HLA result therefore shows genetic compatibility, not the presence of active disease. A negative DQ2 and DQ8 result makes coeliac disease highly unlikely and can help exclude it in selected specialist situations. HLA testing is not recommended as the initial diagnostic test in non specialist settings. It can be useful when someone has already removed gluten, when blood and biopsy results conflict or when specialist evaluation of possible coeliac disease is difficult. Negative blood tests do not always end the investigation Most people with untreated coeliac disease produce detectable antibodies, but a minority do not. If symptoms, anaemia, nutrient deficiency or another feature keeps clinical suspicion high, specialist referral may still be appropriate after negative serology. The specialist may review gluten intake, IgA status, medicines and alternative diagnoses. Endoscopy with duodenal biopsy may be needed to assess possible seronegative coeliac disease or another enteropathy. Seronegative coeliac disease is a specialist diagnosis made only after other causes of villous atrophy have been excluded. The lifelong gluten free diet The only established treatment for ordinary coeliac disease is a strict gluten free diet for life. Removing gluten stops the autoimmune trigger and allows the small bowel lining to heal. The diet applies even when the person has no symptoms after accidental exposure. There is no established tablet, enzyme or supplement that makes regular gluten consumption safe in coeliac disease. Specialist medicines are reserved for rare refractory disease and do not replace a strict gluten free diet. Foods containing gluten Wheat, barley and rye must be excluded. This includes ordinary bread, pasta, cakes, biscuits, pastries, couscous, bulgur, durum, semolina and spelt. Barley malt can appear in cereals, drinks, flavourings and processed foods. Gluten may be present in sauces, gravies, stocks, soups, processed meats and ready meals. Food labels must be checked every time because ingredients and manufacturing processes can change. Naturally gluten free foods Many foods are naturally gluten free. Examples include unprocessed meat, fish, eggs, fruit, vegetables, potatoes, rice, maize, beans, lentils and most dairy products. Gluten free breads, pastas and flours can replace wheat based versions. A gluten free label in the UK means that the product contains no more than the legally permitted trace amount of gluten. A balanced diet remains important because some gluten free replacement products contain less fibre, iron or B vitamins than standard equivalents. Oats Oats contain a protein called avenin rather than the gluten proteins found in wheat, barley and rye. Most people with coeliac disease can tolerate oats that are specifically labelled gluten free. Ordinary oats are frequently contaminated with wheat, barley or rye during growing and processing. A small minority may react even to uncontaminated gluten free oats. Current BSG guidance supports discussing gluten free oats when the gluten free diet begins, with appropriate clinical follow up. Cross contact and accidental exposure Gluten free food can become contaminated through shared toasters, chopping boards, utensils, flour dust, oils or serving equipment. Home, school, workplace and restaurant arrangements may require practical changes. A specialist dietitian can explain proportionate precautions without making food preparation unnecessarily restrictive. Accidental exposure may cause abdominal symptoms, fatigue, headache or no immediate symptoms. One accidental exposure is unlikely to cause permanent harm by itself, but repeated exposure can prevent healing and increase long term risk. The role of a specialist dietitian A dietitian with coeliac expertise helps identify gluten sources, interpret labels and prevent cross contact. They assess nutritional balance, calcium, iron, fibre and vitamin intake. They can also adapt the diet for culture, religion, eating difficulties, pregnancy, diabetes or other medical needs. Dietetic review is especially important when symptoms or antibodies do not improve. Removing more foods without assessment can create malnutrition and may fail to address the true cause of symptoms. Symptom improvement and bowel healing Many digestive symptoms improve within weeks of starting a strict gluten free diet. Anaemia, fatigue, skin disease and neurological symptoms may take longer. Complete small bowel healing can take months or several years, particularly in adults. Symptom resolution does not prove that the intestinal lining has fully healed. Equally, continuing symptoms do not always mean that gluten exposure or active coeliac disease is present. Follow up after diagnosis Current BSG adult guidance recommends regular follow up for up to two years after diagnosis, followed by an individualised longer term plan. Review may include symptoms, weight, dietary adherence, nutritional intake and access to dietetic support. Blood tests can assess iron, folate, vitamin B12, vitamin D, calcium, liver function and other concerns. Coeliac antibody levels often fall after gluten is excluded, but serology alone cannot prove complete dietary adherence or mucosal healing. People with continuing symptoms, complications or difficulty following the diet require closer specialist follow up. Monitoring bone and nutritional health Nutrient deficiencies should be identified and treated rather than supplemented automatically without assessment. Iron, folate, vitamin B12, vitamin D and calcium are particularly relevant. Adults should have bone health assessed according to current specialist guidance and personal fracture risk. Children need continuing review of growth, weight and pubertal development. A person whose diet remains very restricted may need reassessment even when coeliac antibodies have normalised. Vaccination and the spleen Coeliac disease can be associated with reduced splenic function in some adults. The spleen helps protect against particular bacterial infections. Current BSG adult guidance advises pneumococcal vaccination for adults diagnosed with coeliac disease. The GP or vaccination service should apply current national schedules and consider other individual risk factors. Vaccination does not replace the gluten free diet. Persistent symptoms after diagnosis Symptoms can persist because gluten is entering the diet unintentionally. Other possibilities include temporary lactose intolerance, irritable bowel syndrome, microscopic colitis, inflammatory bowel disease, pancreatic disease or another diagnosis. The original coeliac diagnosis may occasionally need to be reviewed. A specialist dietitian should assess hidden gluten and cross contact before the diet is restricted further. Persistent weight loss, diarrhoea, anaemia or nutrient deficiency requires medical investigation rather than repeated self directed food exclusion. Temporary lactose intolerance Lactase is an enzyme located near the tips of the small bowel villi. Villous damage can temporarily reduce lactose digestion and cause diarrhoea, bloating and wind after dairy products. This does not mean that dairy causes coeliac disease or intestinal immune damage. Lactose tolerance often improves as the bowel heals on a gluten free diet. Calcium intake must be protected if dairy products are temporarily reduced. Refractory coeliac disease Refractory coeliac disease is rare. It involves continuing or returning malabsorption and villous atrophy despite a confirmed diagnosis and a strict gluten free diet for a prolonged period. Before making this diagnosis, specialists exclude ongoing gluten exposure, incorrect original diagnosis and more common coexisting conditions. Suspected refractory disease requires referral to an experienced specialist centre. Treatment may involve corticosteroids or other immune modifying medicines alongside the gluten free diet. Risks of untreated disease Continuing gluten exposure can maintain villous damage and malabsorption. Possible consequences include iron deficiency, vitamin deficiency, malnutrition, osteoporosis, fractures and impaired growth. Untreated disease may contribute to subfertility and adverse pregnancy outcomes. Persistent inflammation is associated with a small increased risk of particular cancers. Most people with coeliac disease do not develop cancer, especially when the condition is diagnosed and treated appropriately. Lymphoma and other rare cancers Enteropathy associated T cell lymphoma is a rare cancer associated with coeliac disease, particularly persistent severe or refractory intestinal inflammation. Small bowel adenocarcinoma and some other lymphomas are also slightly more common than in the general population. The absolute risk remains low. A strict gluten free diet and mucosal healing reduce long term risk. New progressive weight loss, persistent abdominal pain, repeated vomiting, gastrointestinal bleeding or unexplained deterioration requires reassessment rather than being attributed automatically to ordinary coeliac symptoms. Coeliac disease and wheat allergy Wheat allergy is an allergic reaction to proteins within wheat. It may cause itching, hives, swelling, wheezing, vomiting or anaphylaxis. Reactions can occur rapidly, although allergy patterns vary. Coeliac disease instead causes a delayed autoimmune injury to the small bowel lining and does not usually cause hives, throat swelling or immediate wheezing. A person with wheat allergy may tolerate barley or rye depending on the specific allergy. A person with coeliac disease must avoid gluten from wheat, barley and rye. Allergy testing and coeliac testing answer different clinical questions. Coeliac disease and non coeliac gluten sensitivity Non coeliac gluten sensitivity describes recurring symptoms associated with gluten containing or wheat containing foods when coeliac disease and wheat allergy have been excluded. There is no validated antibody, biopsy or genetic test that confirms this condition. It does not produce the characteristic coeliac autoantibodies or villous injury. Gluten may not always be the specific trigger. Fructans and other wheat components can contribute to symptoms in some people. Diagnosis requires careful exclusion of other disease and may involve a structured dietetic supervised elimination and reintroduction process. Testing for coeliac disease must be completed before gluten is removed. Coeliac disease and food intolerance Food intolerance usually causes symptoms without the autoimmune intestinal damage of coeliac disease or the immediate immune mechanism of allergy. Lactose intolerance is an example and can occur temporarily during untreated coeliac disease. Symptoms alone cannot reliably distinguish intolerance, allergy, coeliac disease and irritable bowel syndrome. Commercial intolerance tests based on unvalidated antibody panels do not diagnose coeliac disease. Emotional and social effects A strict lifelong diet can affect eating out, travel, education, work and relationships. Fear of cross contact may produce anxiety or social isolation. The cost and availability of safe food can create practical inequalities. Support from a dietitian, family, school, workplace and recognised patient organisations can improve confidence. Dietary safety should be taken seriously without blaming the person for accidental exposure. What this lesson should not be used for This lesson cannot diagnose coeliac disease from bloating, anaemia, a rash or symptom improvement after avoiding bread. Do not begin a gluten free diet before completing appropriate tests unless a specialist has advised it. Do not undertake a gluten challenge after a possible allergic reaction without clinical assessment. Seek medical review for persistent gastrointestinal symptoms, unexplained anaemia, weight loss, bone disease, infertility, neurological symptoms or a strong health problems in the family.

Coeliac disease is an autoimmune injury to the small bowel caused by gluten, not a wheat allergy or ordinary intolerance. It can present through gastrointestinal symptoms, nutrient deficiency, weak bones, dermatitis herpetiformis, infertility, neurological disease or no symptoms. Testing must occur while gluten is still being eaten, and the only established treatment is a strict lifelong gluten free diet.