With the introduction of two new laboratory tests in the last few years, it’s easier to diagnose celiac disease and also to assess one’s genetic risk for celiac disease, an autoimmune inflammatory gastrointestinal disorder also known as gluten sensitivity enteropathy (GSE). According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), celiac disease affects one in 133 people in the United States. It’s estimated that as few as three percent of people with celiac disease have been diagnosed. Although serological antibody tests have been available to aid in diagnosis for more than a decade, intestinal biopsy has traditionally been considered the gold standard. With newer antibody tests, diagnosis with serology tests is now considered a reliable disease indicator.
Autoimmune Component
For an autoimmune disease to develop there must be the following three components:
- a genetic predisposition
- an external trigger, and
- an immune response to the trigger
In celiac disease, the presence of DQ HLA antigens confirms susceptibility to Graves’ disease. Someone without these genes is not at risk for celiac disease. Gluten and gliadin proteins are the triggers in celiac disease. These proteins are found in wheat, rye and barley. Some people with variants of GSE will react to only proteins found in wheat and some will only react to wheat and one of the other grains. However, most people react to all three grain products and it’s recommended that all grains in these families, including hydrolyzed vegetable oils, be avoided. People with gluten intolerance have milder inflammatory reactions to these grains and can develop many of the symptoms seen in celiac disease.
Autoantibodies in Celiac Disease
In celiac disease the tissue transglutaminase (tTG) enzyme produces the dangerous gliadin peptide from gluten. Gliadin then initiates an inflammatory reaction in the small bowel. Gliadin is also dangerous because it resists breakdown in the small intestine and it damages the cells that line the small intestines. In addition, when gliadin is taken up into the lamina propria of the intestines, it forms glutamic acid residues that are expressed to immune system cells. This initiates an inflammatory response.
Antibodies to tTG are considered diagnostic for celiac disease in most cases. In people with symptoms of celiac disease, a positive tTG antibody test is an indication to start a gluten free diet. Endomysial antibody tests are also available but because of their expense, the tTG antibody test is considered superior. Tests for reticulin antibodies are also available but because they are only seen in about 65 percent of patients with celiac disease, this test is falling out of favor. Because people with celiac disease are often deficient in immunoglobulin A (IgA), negative tests for IgA gliadin antibodies in people who are strongly suspected of having celiac disease or who have IgG gliadin antibodies should be followed up with IgA levels.
Deamidated Gliadin Peptide Antibodies
Early tests for gliadin antibodies were useful but not as specific or sensitive as the other antibody assays used for celiac disease. However, the new test for deamidated gliadin peptides (DGP) antibodies, which was introduced in 2007, is an excellent diagnostic tool. Sensitivity and specificity for celiac disease are respectively 83.6 and 90.3% for IgA and 84.4 and 98.5% for IgG antibodies to deamidated gliadin peptides. In studies, DGP antibody tests displayed higher diagnostic accuracy than antigliadin antibody tests and, although less sensitive than antiendomysial and tissue transglutaminase antibodies, tests for DGP antibodies showed significantly higher specificity than tissue transglutaminase antibodies (P < 0.001).
In addition, persistence of peptide antibodies after gluten withdrawal can be interpreted as an expression of low compliance with the diet and of the lack of improvement of the intestinal mucosa. The combined use of tissue transglutaminase and deamidated gliadin peptide antibodies is regarded as a very useful tool for celiac disease diagnosis and follow-up.
Testing Genetic Susceptibility
The new MyCeliac ID saliva-based test by Prometheus Laboratories identifies the specific gene sequence associated with celiac disease. Positive test results confirm genetic risk and are of particular value in families in which first-degree relatives have celiac disease. People who test negative for these genes have a very low likelihood of developing celiac disease. As a direct access test (DAT) individuals can self-order the test kit, send in their saliva samples, and receive secure online results that have been reviewed by a physician.
Sources:
Kelly Graham. 2010. Lab Identification of Celiac Disease. Advance for Administrators of the Laboratory, January: 32-4.
Celiac Disease. National Digestive Diseases Information Clearinghouse. Accessed Feb. 8, 2009.
Celiac Disease Facts and Figures. The University of Chicago Celiac Disease Center. Accessed Feb. 8, 2009.
Elaine Moore - I'm a retired medical technologist and medical writer with more than 30 years experience working in hospital laboratories. Currently, I ...
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