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Diagnostic Testing Algorithms for Celiac Disease



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Diagnosis of Celiac Disease

Slide 6

updated June 2011

As I stated in the last slide, laboratory serology plays a key role in establishing a presumptive diagnosis of celiac disease.

The primary antibodies associated with celiac disease are tissue transglutaminase, or TTG, antibodies; deamidated gliadin antibodies; and endomysial antibodies, or EMA. Testing for TTG and deamidated gliadin antibodies involve testing for IgA and IgG isotypes, while the EMA assay detects only the IgA isotype. The testing methodology is also different. TTG and deamidated gliadin antibodies are detected using plate-based enzyme immunoassays, while EMAs are detected by an immunofluorescent assay using a monkey esophagus substrate. These tests, although different in their methodologies, are related. The EMA assay is so-named because it detects an antigen in the endomysium, which is the connective tissue that surrounds smooth muscle fibers. It was subsequently determined that the antigen target of the EMA was tissue transglutaminase. It was this discovery that led to development of immunoassays specific for TTG. The antibodies against gliadin are related to the dietary gluten that initiates the inflammation in celiac disease. When the protein gluten is ingested, it is digested into smaller peptides. The ethanol-soluble fraction of gluten is referred to as gliadin. The first enzyme immunoassays developed tested for antibodies against gliadin. However, these assays were inferior to the TTG antibody and EMA assays and generally were not recommended. The newest generation of gliadin antibody assays uses a novel form of this antigen, specifically deamidated gliadin. These assays detect antibodies against gliadin that has undergone enzymatic deamidation by tissue transglutaminase. These newer assays specific for deamidated gliadin are similar to the TTG antibody assays in both sensitivity and specificity.

When testing for celiac disease using antibody serology, it is also important to remember that these antibody levels generally will decrease with proper adherence to a gluten-free diet.

Diagnosis of Celiac Disease

 


 

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