A simple blood test is available to screen for celiac disease. People with celiac disease who eat gluten have higher than normal levels of certain antibodies in their blood. These antibodies are produced by the immune system because it views gluten (the proteins found in wheat, rye and barley) as a threat. You must be on a gluten-containing diet for antibody (blood) testing to be accurate.
Who should get screened?
- Children older than 3 and adults experiencing symptoms of celiac disease
- First-degree relatives of people with celiac disease (parent, child, sibling)
- Any individual with an associated autoimmune disorder or other condition, especially type 1 diabetes mellitus, autoimmune thyroid disease, autoimmune liver disease, Down syndrome, Turner syndrome, Williams syndrome, and selective immunoglobulin A (IgA) deficiency
The First Step: tTG-IgA Test
There are many screening blood tests for celiac disease but the most sensitive and commonly used, whether symptoms are present or not, is the tTG-IgA test. All celiac blood tests require that you be on a gluten-containing diet to be accurate.
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. Though rare, this means patients with celiac disease could have a negative antibody test result.
There is also a slight risk of a false positive test result, especially for people with associated autoimmune disorders like Type 1 Diabetes, autoimmune 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, but because of potential for false antibody test results, a biopsy of the small intestine is the only way to diagnose celiac disease.
- 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.
If you are currently on a gluten-free diet, your physician may recommend a gluten challenge to allow antibodies to build in your bloodstream prior to testing. Recommendations range from eating 1/2 slice of bread or a cracker daily for 12 weeks to eating 3 grams of gluten for 2 weeks. A gluten challenge should only be supervised by a physician trained in celiac disease, who can move you immediately to a biopsy if your symptoms are severe. Never undertake a gluten challenge when pregnant.
People with celiac disease carry one or both of the HLA DQ2 and DQ8 genes. So do up to 25-30% of all people. Carrying HLA DQ2 and/or DQ8 is not a diagnosis of celiac disease nor does it mean you will ever develop celiac disease. However, if you carry HLA DQ2 and/or DQ8 your risk of developing celiac disease is 3% instead of the general population risk of 1%.
Since celiac disease is genetic, this means it runs in families. First-degree family members (parents, siblings, children), who have the same genotype as the family member with celiac disease, have up to a 40% risk of developing celiac disease. The overall risk of developing celiac diseaes when the genotype is unknown is 7% to 20%.
Who Should Have Celiac HLA Testing?
- Those on a gluten-free diet – celiac antibody blood testing is not accurate
- When diagnosis of celiac disease is not clear
- ambiguous antibody testing results (especially in children under the age of 3)
- equivocal intestinal biopsy results
- discrepancy between antibody and biopsy findings
- Family members of people with celiac disease to evaluate risk
- a negative result assures a 99% probability that the family member will NOT develop celiac disease
- a positive result indicates the family member should follow up with celiac antibody testing every 2-3 years or immediately if symptoms develop
How Do I Get Tested?
Your physician should be able to order genetic testing. Genetic testing can be done by blood test, saliva test or cheek swab.
Genetic testing is expensive with the cost running in the hundreds of dollars, but may be covered by some insurance plans. First-degree family members unsure about the expense should weigh this against the time and expense of undergoing life-time serologic testing.
Keep in mind that positive antibody results combined with positive genetic 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 an endoscopic biopsy of the small intestine.
The gluten-free diet is currently the ONLY treatment for celiac disease and non-celiac wheat sensitivity. Once diagnosed, you will immediately need to eliminate all wheat, rye and barely products from your diet. Ingesting small amounts of gluten, like crumbs from a cutting board or toaster, can trigger intestinal damage.
Once diagnosed, annual follow-up with your physician is necessary to monitor nutritional deficiencies and your compliance with a gluten-free diet, as well as assess for associated conditions.
Finding the Right Doctor
Celiac Disease Foundation can help you find the right doctor to discuss symptoms, diagnose, and treat celiac disease. Our nationwide Healthcare Practitioner Directory lists primary care physicians and specialists,and dietitians and mental health professionals, experienced in celiac disease and non-celiac wheat sensitivity.