Coeliac Disease Tests

Coeliac disease tests are used to screen for and help diagnose coeliac disease and a few other gluten-sensitive conditions (such as dermatitis herpetiformis). 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. Since patients with such symptoms may have different underlying conditions such as food allergy or lactose intolerance, coeliac tests may be done in conjunction with testing for food intolerance and food allergy.

Sometimes coeliac testing is used to screen for coeliac disease where is shows no symptoms in those who have close relatives with coeliac disease (about 10% of those who have close relatives with coeliac disease will develop it themselves) and/or in those who have other autoimmune diseases such as type 1 diabetes mellitus, or thyroid disease (patients with autoimmune diseases often have more than one autoimmune disease).

A doctor may use one or more coeliac disease tests, along with tests to evaluate the status and extent of a patient’s malnutrition and malabsorption. Nowadays there are two main autoantibodies that are related to celiac disease that can be measured. The doctor will often request an anti-tissue Transglutaminase Antibody (TTG), IgA or an antiendomysial antibody (EMA), IgA initially. Sometimes patients can initially be tested by TTG testing, and positive results confirmed on EMA testing. If the initial screening anti-TTG, IgA is moderately or strongly positive, or both tests (TTG, IgA and EMA, IgA) are positive, it is likely that the patient has coeliac disease. The doctor may then arrange an intestinal biopsy to confirm that there is damage to the intestine – this is the gold standard for diagnosis. Sometimes the patient’s history and autoantibody tests are so suggestive of celiac disease, that the biopsy may not always be essential.

If the anti-TTG and anti-EMA are negative but the doctor still suspects celiac disease, they may request other tests that include:

• repeat anti-TTG, IgA and anti-EMA, IgA antibodies
• serum IgA level, as about 2-3% of coeliac disease patients are IgA-deficient
• anti-TTG, IgG autoantibodies if serum IgA is low or absent
• anti-gliadin antibodies (AGA), IgG and IgA. These tests are often useful when testing young symptomatic children. They are not useful in adults because they are found in fewer cases of celiac disease than anti-TTG (lower sensitivity) and they can also be positive in other abdominal diseases (lower specificity)

Measurement of anti-EMA, IgA and/or anti-TTG, IgA antibodies can also be used for monitoring compliance with a gluten-free diet, as they disappear several weeks or months after this is started. However they will remain positive if gluten continues to be present in the diet. 

The above autoantibody tests are often used along with other tests to help determine the severity of the disease and the extent of a patient’s malnutrition, malabsorption, and organ involvement. Other tests might include a:

• FBC (full blood count) to look for anaemia
• ESR (erythrocyte sedimentation rate) to evaluate inflammation
• CRP (C-Reactive protein) to evaluate inflammation
• Biochemistry testing to determine sodium, potassium, calcium, and protein levels, and to check kidney and liver function
• Iron, folate, vitamin B12, D, E to check for mineral and vitamin deficiencies
• On rare occasions, stool fat levels, to help evaluate malabsorption

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. They may be ordered as part of an investigation of anaemia, osteoporosis, and less often infertility, or neurological symptoms (ataxia and certain types of seizure are linked to coeliac disease).   

In children, coeliac disease tests may be requested when a child exhibits delayed development, short stature and/or a failure to thrive.  

People who do not have symptoms may be tested if they have a close relative with coeliac disease, or another autoimmune disease, but coeliac disease testing is not recommended at this time as a screen for the general population.  

Autoantibody levels (anti-TTG, IgA; anti-EMA, IgA) may also be checked when a patient with coeliac disease has been on a gluten-free diet for a period of time. This is done to verify that antibody levels have decreased after commencing the diet. The improvement in the symptoms, together with disappearance of the autoantibodies is a good marker of improvement in the inflammation in the gut wall. 

When a patient’s symptoms have not subsided, coeliac disease tests may be used to check for dietary compliance, and if they remain positive they may guide the doctor and patient to look either for hidden gluten in the patient’s diet or for other reasons for their unrelieved symptoms.

In general, if your anti-TTG test is at least moderately or strongly positive, then it is likely that you have coeliac disease. False positive results can however be found and this is the reason for checking anti-EMA, IgA, and sometimes performing a small intestinal biopsy.  

If the anti-TTG, IgA test is negative, then it is most likely that you do not have coeliac disease. However, your anti-TTG, IgA levels 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 small percentage of patients with coeliac disease who are also deficient in IgA. This may lead to a false negative result and may prompt your doctor to do additional testing.  

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 if the blood test results are equivocal, your doctor may consider an intestinal biopsy to confirm or rule out celiac disease.  

If you have been diagnosed with coeliac disease and have removed gluten from your diet, then your autoantibody levels 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 celiac disease tests are used to monitor progress, rising levels 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 Europe 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 -- they may be mild or even absent, even when intestinal damage is present in the bowel wall. Since these symptoms may also be due to a variety of other conditions a diagnosis of coeliac disease may be missed or delayed -- sometimes for years.