A simple blood test is available to test 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 should be tested
- First-degree relatives of people with celiac disease – parents, siblings and children have a 1 in 10 risk compared to 1 in 100 in the general population
- 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
Testing for Celiac Disease in Children Under the Age of 3
From the University of Chicago Celiac Disease Center:
“Generally, children at risk for celiac disease are screened at age 2 or 3 unless symptoms are seen beforehand. In children younger than 3, with symptoms, antibody testing may not always be accurate.
Children must be eating wheat or barley-based cereals for some time, up to one year, before they can generate an autoimmune response to gluten that shows up in testing. A pediatric gastroenterologist should evaluate young children experiencing a failure to thrive or persistent diarrhea for celiac disease.
While a genetic test cannot diagnose celiac disease by itself, it can all but rule it out if neither of the genes are present, and a genetic test can be done at any age.”
The First Step:
For most children and adults, the best way to test for celiac disease is with the Tissue Transglutaminase IgA antibody, plus an IgA antibody in order to ensure that the patient generates enough of this antibody to render the celiac disease test accurate.
For young children (around age 2 years or below), Deamidated Gliadin IgA and IgG antibodies should also be included. All celiac disease 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. The test’s sensitivity measures how correctly it identifies those with the disease. The same test will come back negative in about 95% of healthy people without celiac disease. The test’s specificity refers to how accurately it is able to identify those without the disease. The tTG test is the most sensitive test for celiac disease. 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%, making it the most specific test for celiac disease, although it is not as sensitive as the tTG-IgA test.2 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 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.
Deamidated gliadin peptide (DGP IgA and IgG): This test can be used to further screen for celiac disease in individuals with IgA deficiency, which affects 2-3% of patients with celiac disease, or people who test negative for tTg or EMA antibodies. IgA deficiency in a patient may be indicative of other diseases that may cause villus atrophy, such as giardiasis, small-bowel bacterial overgrowth (SIBO) or common variable immunodeficiency (CVID).2
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.
Video capsule endoscopy (VCE): VCE has a sensitivity of 89% and specificity of 95% for celiac diagnosis. This method of testing is more sensitive at detecting macroscopic atrophies in comparison with regular upper endoscopy (92% vs. 55%). VCE is also useful in detecting complications linked with celiac disease.2
Intestinal fatty acid binding protein (I-FABP): When cellular damage occurs, this cytosolic protein is released into the systemic circulation of blood and could indicate unintentional gluten intake.2
Radiology: Some radiological findings may indicate the presence of celiac disease, e.g., small-bowel dilation, wall thickening, vascular changes, and others.2
The Gluten Challenge
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. NASPGHAN recommends eating roughly 2 servings of gluten, equivalent to 2 slices of wheat-based bread, daily for 6-8 weeks prior to testing. The Celiac Disease Center at the University of Chicago recommends eating gluten every day, in an amount equivalent to at least 1 slice of bread, for at least 2 to 3 weeks prior to undergoing biopsy. Please consult with your gastroenterologist regarding your gluten challenge.
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. A gluten challenge is not recommended before the age of 5 or during puberty.2 Never undertake a gluten challenge when pregnant.
People with celiac disease carry one or both of the HLA DQ2 and DQ8 genes, but so does up to 25-30% of the general population. 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.