Celiac Disease Tests
Celiac disease tests help determine whether you have celiac disease and to monitor compliance to and the effectiveness of a gluten-free diet. Symptoms of celiac disease may include chronic diarrhea, abdominal pain, anemia, and weight loss. It is sometimes done when an infant is chronically irritable or fails to grow at a normal rate. Occasionally the test is used to monitor treatment of celiac disease.
Celiac disease tests are a group of assays developed to help diagnose celiac disease and a few other gluten-sensitive conditions. These tests detect autoantibodies that the body creates as part of an immune response to dietary proteins (gluten and gliadin) found in wheat, rye, and barley. These autoantibodies cause intestinal inflammation and damage in the lining of the intestinal wall. This causes symptoms associated with malnutrition and malabsorption, such as: diarrhea, weakness, weight loss, abdominal pain, abdominal distention, fatigue, oral ulceration, bleeding tendency, bone and joint pain, and anemia. Adults may also experience depression and a general feeling of illness while children are frequently irritable and may have delayed growth and development.
In the past the only way to diagnose celiac disease was with a biopsy of the small intestine. While this microscopic evaluation is still considered the gold standard and is still used to confirm a diagnosis of celiac disease, the availability of less invasive blood tests used to screen for celiac disease have reduced the number of biopsies needed. Autoantibody blood tests that are available include:
Anti-tissue Transglutaminase Antibody (tTG), IgA: Tissue transglutaminase is an enzyme responsible for cross-linking certain proteins. It has been identified as the antigen that the body responds to when it creates Anti-EMA antibodies. Gliadin in grains triggers the development of tTG autoantibodies. Although "tissue" is in the name of this autoantibody, it nevertheless involves testing blood and not tissue.
Anti-Endomysial Antibodies (EMA), IgA: Endomysium is the thin connective tissue layer that covers individual muscle fibers. Anti-Endomysial antibodies are developed in reaction to the ongoing damage to the intestinal lining. Almost 100% of patients with active celiac disease and 70% of patients with dermatitis herpetiformis (another gluten-sensitive enteropathy that causes an itchy burning blistering rash on the skin) will have Anti-EMA, IgA antibodies. Anti-tTG and Anti-EMA antibodies measure the same tissue damage.
Anti-Gliadin Antibodies (AGA), IgG and IgA: Gliadin is part of the gluten protein found in wheat (similar proteins are found in rye, barley, and oats). AGA is an autoantibody against the gliadin portion. It is created by those who are sensitive to it when they are exposed to gluten over a period of time.
Anti-Reticulin Antibodies (ARA), IgA: Anti-ARA is not ordered as frequently as it once was as it is not as specific or sensitive as the other autoantibodies. It is found in about 60% of celiac disease patients and about 25% of patients with dermatitis herpetiformis. When used, ARA is ordered along with other celiac disease tests to help diagnose celiac disease.
Each of the celiac blood tests available measures the amount of a particular autoantibody in the blood and is available in both an IgG and an IgA version. IgG and IgA are 2 of the five classes of antibody proteins that the immune system creates in response to a perceived threat.
While both IgG and IgA types of each autoantibody will be present in the blood they are not equally specific for celiac disease. In general, the IgA forms of the tests tend to be more specific, and in some cases are used almost exclusively. IgG versions may be ordered either to complement the IgA testing and/or ordered because someone has an overall deficiency in IgA. This happens about 2% of the time with celiac disease and can lead to some false negative test results.
PREPARATION FOR TEST
A blood sample is obtained by inserting a needle into a vein in the arm.
Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.
MEANING OF TEST
Your caregiver will go over your test results with you and discuss the importance of this test. Reference values are dependent on many factors, including patient age, gender, sample population, and testing method. Numeric test results have different meanings in different labs. Your lab report should include the specific reference range for your test.
In general, if your Anti-tTG test is positive, then it is likely that you have celiac disease. If the Anti-tTG test is negative, then it is most likely that you do not have celiac disease. However, your Anti-tTG 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 celiac 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 several of the other autoantibodies are present in high concentrations but tTG is negative, then you may have celiac disease. If only one autoantibody is high, or if one or more are present, but only at low concentrations, then your symptoms may be due to celiac disease or due to another cause. If any of the blood test results are positive (or indeterminate) your caregiver will usually do an intestinal biopsy to confirm or rule out celiac disease.
If you have been diagnosed with celiac 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). A Registered Dietitian can help you identify sources of gluten in your diet. In most cases, when celiac disease tests are used to monitor progress, rising levels of autoantibodies indicate some form of noncompliance with a gluten-free diet.
If you have changed your diet, eliminating gluten days or weeks prior to visiting your caregiver, then your celiac disease may not be detectable. In this case your caregiver 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 do a biopsy to check for villous atrophy (damage to the villi in your intestine).
OBTAINING THE TEST RESULTS
It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.