Coeliac Disease Tests

1. For the diagnosis of patients

Coeliac disease tests are used to screen for and help diagnose or exclude coeliac disease. They are usually requested on those patients with symptoms suggesting coeliac disease, but may also be requested to help rule out coeliac disease as a cause for conditions such as anaemia and abdominal pain.

Testing may be performed to screen for coeliac disease in people who do not have symptoms, but who do have close relatives with coeliac disease. About 10% of people who have close relatives with coeliac disease will develop it themselves.

Coeliac disease tests may also be requested in people who have other autoimmune diseases such as type 1 diabetes mellitus, or thyroid disease as patients with autoimmune diseases often have more than one autoimmune disease.

Testing may also be carried out in patients with metabolic bone disorders (e.g.; osteoporosis or pathological fractures), unexplained neurological symptoms and unexplained reproductive health problems (e.g.; subfertility, recurrent miscarriages)

A doctor may use one or more coeliac disease tests, along with other tests to evaluate the status and extent of a patient’s malnutrition and malabsorption.(e.g.; calcium, vitamin D, haemoglobin, vitamin B12 and folate)

Total immunoglobulin A (IgA) and IgA Anti-tissue Transglutaminase Antibody (tTG) are usually the first choice tests performed for diagnosis of coeliac disease. IgA deficiency is significantly more common in people with coeliac disease in general population. That may give a false negative result when tested for IgA tTG, which may lead to a missed diagnosis. That explains the main reason for performing these two tests together If the results of the tests described above are uncertain, then the next test that may be performed is IgA antiendomysial antibody (EMA). This can be a helpful test when the IgA tTG result is weakly positive.

The final tests that may be used are IgG EMA, IgG deamidated gliadin peptide or IgG anti tTG. These may be performed if IgA deficiency is confirmed.

If the results of autoantibody testing are positive, or if clinical suspicion remains high despite of negative findings, the patient should be referred to a gastrointestinal specialist to undergo biopsy of the small intestine (gut) to confirm or exclude the diagnosis of coeliac disease.

Some other tests may be performed to help determine the severity of the disease and the extent of a patient’s malnutrition, malabsorption, and organ involvement. These might include a:

• FBC (full blood count) to look for anaemia
• CRP (C-Reactive protein) to evaluate inflammation
• Biochemistry testing to determine sodium, potassium, calcium, and protein concentrations, and to check kidney and liver function
• Iron, folate, vitamin B12, vitamin D to check for mineral and vitamin deficiencies

2. For monitoring diagnosed patients with coeliac disease

When a patient with coeliac disease has been on a gluten-free diet for a period of time, autoantibody concentrations should decrease. The improvement in symptoms, together with disappearance of the autoantibodies from the blood is a good marker of improvement in the inflammation in the gut wall. However, blood testing alone is not used to determine whether gluten has been excluded from the patient’s diet. It includes measuring weight (and height if a child), reviewing symptoms and looking for other complications. When a patient’s symptoms have not subsided and coeliac disease tests remain positive further actions may be necessary. Intestinal biopsy is an investigation that is helpful in this situation. Some patients are diagnosed as having refractory coeliac disease, which needs specialist advice and further investigations.

Coeliac disease tests are requested:

• when someone has symptoms suggesting coeliac disease, malnutrition, and/or malabsorption - such as diarrhoea, abdominal pain, bloating, weakness, fatigue, and weight loss
• during the investigation of a wide range of conditions such as anaemia, osteoporosis, unexplained subfertility or recurrent miscarriages, unexplained neurological symptoms, and raised liver enzymes with unknown cause
• in children, when there is delayed development, short stature and/or a failure to thrive
• if someone has a close relative with coeliac disease
• if someone has an autoimmune disease, such as type 1 diabetes mellitus, or thyroid disease
• if someone has Down or Turner syndrome
• to monitor the success of a gluten free diet

Currently coeliac disease testing is not recommended as a screen for the general population.

In general, if your anti-tTG test result is at least moderately or strongly positive, then it is likely that you have coeliac disease. However, a positive anti –tTG test alone is not sufficient for diagnosis. Confirmation is necessary with a second test, either a blood test or an intestinal biopsy.

If the anti-tTG IgA test result is negative, then it is most likely that you do not have coeliac disease. However, your anti-tTG IgA concentrations may be very low or undetectable if you have been avoiding wheat, rye, and barley for a period of time or if you are one of the patients with coeliac disease who are also deficient in IgA. This may lead to a false negative result and may prompt your doctor to request IgA anti-EMA.

If the anti-EMA IgA is positive but the anti-tTG IgA autoantibody is negative, then it is still possible you may have coeliac disease. Hence your doctor may consider additional antibody testing with IgG EMA, IgG DPG or IgG anti-tTG. Usually, intestinal biopsy is the last option to confirm or rule out coeliac disease if these tests are still negative.

If you have been diagnosed with coeliac disease and have removed gluten from your diet, then your autoantibody concentrations should fall. If they do not, and your symptoms do not diminish then there may either be hidden forms of gluten in your diet that have not been eliminated (gluten is often found in unexpected places, from salad dressings to cough syrup) or you may have one of the rare forms of coeliac disease that does not respond to dietary changes. In most cases, when coeliac disease tests are used to monitor progress, rising concentrations of autoantibodies indicate some form of non-compliance with a gluten-free diet.

If you have changed your diet, eliminating gluten days or weeks prior to visiting your doctor, then your coeliac disease autoantibodies may not be detectable. In this case your doctor may do a gluten challenge – have you put gluten back into your diet for several weeks or months to see if the symptoms return, then recheck autoantibodies, and consider whether a biopsy of the intestine is necessary.

Although coeliac disease is relatively common (about 1 in 100 people in the UK are thought to be affected) most people who have the disease are not aware of it. This is partly due to the fact that the symptoms are variable and may be mild or absent, even when intestinal damage is present in the gut wall. Since these symptoms may also be due to a variety of other conditions a diagnosis of coeliac disease may be missed or delayed.

People may develop allergies to any foods, including cereals such as wheat and rye. Genuine food allergies involve immediate reactions and the production of specific IgE antibodies. These IgE antibodies if produced in response to wheat or rye may cause some symptoms similar to those caused by coeliac disease but they will only do so for a short time after eating the triggering food. The reaction may be mild or severe but does not cause chronic damage to the lining of the intestine in the same way that coeliac disease does. Symptoms of food allergy may not be confined to the gut, and can cause rashes, swelling such as of the face, and in the worst cases a severe allergic reaction (anaphylaxis). If you feel that you may have wheat or other grain allergy, talk to your doctor. They can arrange a blood test for these specific IgE antibodies, or arrange referral to an allergy specialist who can perform a more detailed assessment and undertake skin prick testing. It is important to know also that false positive specific IgE antibodies can be found in patients with grass-pollen hay fever.