Celiac Disease Screening
May 1, 2015
A simple blood test is available to screen for celiac disease antibodies. People with celiac disease who eat gluten have higher than normal levels of these antibodies in their blood. You must be on a gluten-containing diet for antibody (blood) testing to be accurate.
The First Step: tTG-IgA Test
Tissue Transglutaminase Antibodies (tTG-IgA) – The tTG-IgA test will be positive in about 98% of patients with celiac disease who are on a gluten- containing diet. This is called the test’s sensitivity. The same test will come back negative in about 95% of healthy people without celiac disease. This is called the test’s specificity. There is a risk of a false positive especially for people with associated autoimmune disorders like Type 1 diabetes, chronic liver disease, Hashimoto’s thyroiditis, psoriatic or rheumatoid arthritis and heart failure, who do not have celiac disease.
There are other antibody tests available to double-check for potential false positives or false negatives.
- IgA Endomysial antibody (EMA): The EMA test has a specificity of almost 100%, but is not as sensitive as the tTG-IgA test. About 5-10% of people with celiac disease do not have a positive EMA test. It is also very expensive in comparison to the tTG-IgA and requires the use of primate esophagus or human umbilical cord. It is usually reserved for difficult to diagnose patients.
- Total serum IgA: This test is used to check for IgA deficiency, a harmless condition associated with celiac disease that can cause a false negative tTG-IgA or EMA result. If you are IgA deficient, your doctor can order a DGP or tTG-IgG test.
- Deaminated gliadin peptide (DGP IgA and IgG): This test can be used to further screen for celiac disease in individuals with IgA deficiency or people who test negative for tTg or EMA antibodies.
While it is very rare, it is possible for someone with celiac disease to have negative antibody test results. If your tests were negative, but you continue to experience symptoms, consult your physician and undergo further medical evaluation.
People with celiac disease carry one or both of the HLA DQ2 and DQ8 genes. So do up to 40% of all people. Since only 1% of us has celiac disease, carrying HLA DQ2 or DQ8 is not a diagnosis of celiac disease nor does it mean you will ever develop celiac disease.
Genetic testing can be used to rule out celiac disease when a patient is already on a gluten-free diet or test results are inconclusive, and to encourage first degree relatives to get antibody testing (every 3 years or immediately if symptoms develop). Genetic testing can be done by blood test, saliva test or cheek swab.
Keep in mind that positive antibody or genetic test results only suggest the presence of celiac disease—the test results cannot confirm it. If these screening tests come back positive, the next step in diagnosing celiac disease is to get a biopsy of the small intestine.