An article in Clinical Gastroenterology and Hepatology offers a series of practical suggestions for using serology testing to diagnose celiac disease (CD), and which deficiencies individuals should be assessed for once they’re diagnosed.
CD is a well-known topic among the medical community, yet the diagnostic path for this condition hasn’t always been clear. Specifically, “confusion abounds regarding the use and interpretation of diagnostic tests, which are often confounded by adoption of the gluten-free diet (GFD),” according to gastroenterologists at the Mayo Clinic’s Division of Gastroenterology and Hepatology, who authored the article.
The authors leveraged their clinic experiences with CD to advise gastroenterologists about testing for and following up with patients who have this condition. This includes a “how to” for using serologic tests to diagnose CD, a genre of testing that has progressed rapidly during the last 20 years.
“The long-used anti-gliadin antibodies have been supplanted by serology with better test characteristics. For example, endomysial antibody (EMA), used for more than 20 years, has specificity of 99%, although the sensitivity varies because of the technical issues inherent in direct immunofluorescence,” the article stated.
Immunoglobulin A tissue transglutaminase (IgA-based TTG), a test that ranks high on sensitivity and specificity, is the best serologic test for detecting CD in patients, particularly those who still consume gluten. The authors note that the test does have some limitations, however.
“It is well-known that IgA deficiency affects 2%–3% of CD patients and occurs in 1:131 patients tested for CD4; thus, IgA-based assays alone are not always reliable. To avoid missing IgA deficient CD, a serologic cascade testing starting with
serum IgA level can be performed, and if normal, an IgA
TTG is adequate; however, if the IgA level is low or absent,
IgG-based testing with deamidated gliadin peptide (DGP) and/or TTG could be added/substituted,” they recommended.
Other serologic testing alternatives include DGP antibody, the newest of the markers for CD, and point-of-care fingerstick TTG antibody testing, although the sensitivity readings for each of these tests aren’t as strong as the specificity. The fingerstick test, for example, “has been developed as a rapid screen for CD, and although the specificity was reportedly 100%, the sensitivity was only 82%. It cannot be recommended until sensitivity improves,” the authors stated.
Moving from testing procedures to protocols, the Mayo Clinic’s gastroenterologists recommend that any first-degree relatives of CD patients get tested—even if they show no symptoms. This especially applies to siblings. “Providers should, at minimum, assess for clinical features of CD among relatives. In families with affected sib pairs, all first-degree and second-degree relatives should be tested.”
Other patients at increased risk for CD also should undergo testing. The authors suggest using serology to test for CD in patients with T1DM and HLA haplotyping for those with chromosomal abnormalities like trisomy 21. “In these patients, diagnostic testing should be the terminology used rather than screening to ensure insurance coverage,” the authors recommended.
Once patients receive a diagnosis of CD, an important next step for gastroenterologists is to assess these patients for various deficiencies. Iron deficiency anemia and bone disease are often seen in CD patients, as are low levels of folate and B12. Some deficiencies can lead to neurologic problems if unchecked.
Recommended tests include: complete blood count, ferritin, vitamin B12, folate, copper, zinc, calcium, 25-hydroxy vitamin D, and bone densitometry.