Coeliac disease (celiac disease): symptoms, testing and the gluten-free diet

The NHS says symptoms of coeliac disease can range from mild to severe and often come and go. Mild cases may not cause any noticeable symptoms, and the condition is then often only detected during testing for another condition. Treatment is recommended even when symptoms are mild or absent, because complications can still occur.

Eating foods that contain gluten can trigger the gut symptoms below. The NHS says diarrhoea is common and is caused by the small bowel not being able to absorb nutrients, which can make stools foul-smelling, greasy and frothy.

• Diarrhoea, which may smell particularly unpleasant.

• Stomach aches, bloating and farting (flatulence).

• Indigestion, constipation and sometimes vomiting.

• Tiredness (fatigue), which may be a sign of iron, vitamin B12 or folate deficiency anaemia.

• Unintentional weight loss.

• An itchy rash (dermatitis herpetiformis). The NHS estimates around 1 in 4 people with coeliac disease develop it.

• Problems getting pregnant (infertility).

• Tingling and numbness in the hands and feet (peripheral neuropathy), and problems with co-ordination, balance and speech (ataxia).

The NHS says coeliac disease is an autoimmune condition, in which the immune system mistakenly attacks healthy tissue. The immune system mistakes substances inside gluten as a threat and attacks them, which damages the surface of the small bowel and disrupts the body's ability to take in nutrients from food.

Gluten is a dietary protein found in three cereals: wheat, barley and rye. It is found in any food that contains them, including pasta, cakes, breakfast cereals, most types of bread, certain sauces and some ready meals. Most beers are made with barley.

Coeliac UK stresses that it is a serious autoimmune condition, not an allergy or food intolerance. It says the reaction damages the lining of the gut (the villi), where food and nutrients are absorbed, and that the only treatment is a strict gluten-free diet for life.

The NHS says coeliac disease is treated by excluding foods containing gluten from your diet for life. Even a small amount, such as a spoonful of pasta, may cause very unpleasant intestinal symptoms, and eating gluten regularly puts you at greater risk of complications such as osteoporosis and some types of cancer in later life.

When you are first diagnosed the NHS says you will be referred to a dietitian to help you adjust and make sure your diet is balanced. Gluten is not essential in your diet, and many gluten-free versions of bread, pasta and pizza bases are available. The NHS says some GPs may provide bread and flour mixes on prescription.

The NHS says that by law food labelled as gluten-free can contain no more than 20 parts per million (ppm) of gluten, and that for most people with coeliac disease these trace amounts will not cause a problem. It advises always checking labels and says many people accidentally eat gluten in the first few months after diagnosis, which may bring symptoms back.

On oats, the NHS says they do not contain gluten, but many people with coeliac disease avoid them because they can become contaminated with other cereals that contain gluten. It says a very small number of people may be sensitive to pure oats because of a protein called avenin. If you want to include oats after discussing this with a healthcare professional, check they are pure and labelled gluten-free.

The NHS says testing involves a blood test, and you may also need a biopsy of the small intestine to confirm the diagnosis. A GP arranges a blood test to check for antibodies usually present in people with coeliac disease. NICE says laboratories should test total immunoglobulin A (IgA) together with IgA tissue transglutaminase (tTG) as the first choice.

If antibodies are found, the NHS says the GP refers you to a gastroenterologist, who may arrange more blood tests or a biopsy. It adds that it is sometimes possible to have coeliac disease and not have these antibodies, so a GP may still refer you if symptoms continue after a negative test.

A biopsy is done in hospital, usually by a gastroenterologist. A thin, flexible tube with a light and camera (an endoscope) is passed through the mouth to the small intestine, after a local anaesthetic to numb the throat and perhaps a sedative. Tiny samples of the lining are examined under a microscope.

After diagnosis, the NHS says you may have further blood tests to check iron and other vitamins and minerals, a skin biopsy if an itchy rash suggests dermatitis herpetiformis, and a DEXA scan if a GP thinks your bones may have been affected.

Both the NHS and NICE are firm on this point. The NHS says that while being tested you need to eat foods containing gluten to ensure the tests are accurate, and you should not start a gluten-free diet until the diagnosis is confirmed by a specialist, even if blood test results are positive.

NICE advises people who are following a normal diet to eat some gluten in more than 1 meal every day for at least 6 weeks before testing. NICE also advises against offering serological testing for coeliac disease in infants before gluten has been introduced into the diet.

The NHS says routine testing for coeliac disease is not done in England. Testing is usually only recommended for people who have symptoms or an increased risk. It says you should be tested if you have any one of the following.

• Persistent unexplained gastrointestinal symptoms such as diarrhoea, stomach ache and bloating.

• Faltering growth.

• Prolonged tiredness all the time (fatigue).

• Unintentional weight loss.

• Severe or persistent mouth ulcers.

• Unexplained iron deficiency anaemia, or vitamin B12 or folate deficiency anaemia.

• Type 1 diabetes.

• Autoimmune thyroid disease, including an underactive or overactive thyroid.

• Irritable bowel syndrome (in adults).

• A first-degree relative (parent, sibling or child) with coeliac disease.

The NHS says it is not entirely clear what causes the immune system to act this way, but a combination of genetics and the environment appears to play a part. Coeliac UK describes it as a genetically linked condition.

The NHS says reported cases are higher in women than men and that it can develop at any age. People with type 1 diabetes, autoimmune thyroid disease, Down's syndrome and Turner syndrome have an increased risk, as do first-degree relatives of someone with the condition.

The NHS says children with coeliac disease may not grow at the expected rate in height and weight, and may have delayed puberty. Faltering growth is one of the reasons it lists for coeliac testing.

The NHS advises not to introduce gluten into a baby's diet before they are 6 months old, and notes that breast milk and all infant milk formulas are naturally gluten-free. NICE advises against testing infants before gluten has been introduced into the diet.

Coeliac UK says that once one person in a family is diagnosed, the rest of the immediate family should be tested.

The NHS says complications of coeliac disease only tend to affect people who continue to eat gluten or have not yet been diagnosed. It says it is a common misconception that eating a little gluten will not harm you.

Possible complications listed by the NHS include osteoporosis, iron deficiency anaemia and vitamin B12 or folate deficiency anaemia, malnutrition in severe cases, and lactose intolerance in untreated disease that usually improves on a gluten-free diet. Cancer is described as a very rare but serious complication; the NHS says the risk is slightly increased and that once you have been following a gluten-free diet for some time, your risk is the same as that of the general population. Poorly controlled coeliac disease in pregnancy can increase the risk of complications such as a baby with a low birth weight.

NICE says to offer an annual review to people with coeliac disease. The NHS says the review covers height and weight, symptoms, your diet and whether you need further nutritional help. The NHS also says that if coeliac disease has affected your spleen you may need extra vaccinations such as the flu and pneumococcal vaccines.

On the NHS, testing starts with your GP, who arranges the blood test and refers you to a gastroenterologist if antibodies are found. Dietitian support and an annual review are part of NHS follow-up, and the NHS says some GPs may provide gluten-free bread and flour mixes on prescription.

Some people choose to see a private gastroenterologist, often for quicker access to blood tests, endoscopy and biopsy. The testing rules are the same in either setting: keep eating gluten until the diagnosis is confirmed. Make sure results and the plan are shared with your GP so the annual review is not missed.