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November 2005
Feature Story
CAP TODAY published an article in November 2000 about Nancy Cornish, MD,
director of microbiology, Methodist Hospital and Children’s Hospital,
Omaha, who is working to improve physician test-ordering. She teaches
Methodist’s physicians about lab tests through periodic clinical
briefs, which she writes and distributes. The response of CAP TODAY readers
to Dr. Cornish’s work was so enthusiastic and the requests for copies
of her briefs so numerous that we asked her to share the clinical briefs
she writes as they become available. Here, this month, is her word on
celiac disease.
New consensus guidelines from the National Institutes of Health recommend serologic
screening and, if positive, confirmation with small bowel biopsy. Based on these
recommendations, the laboratory now offers a celiac disease reflexive panel
that provides sensitive, specific, cost-effective serologic testing in patients
clinically suspected to have celiac disease.
Celiac disease and dermatitis herpetiformis, a skin disease, the two forms
of gluten-sensitive enteropathy (GSE), are characterized by intolerance to gluten,
the protein of wheat, rye, and barley. Classic celiac disease in adults is characterized
by gastrointestinal complaints and changes secondary to malabsorption caused
by immune-mediated injury of the small bowel. Symptoms may include abdominal
discomfort, diarrhea, flatulence, bloating, steatorrhea, weight loss, fatigue,
and malaise. Other people may have atypical, silent, or latent celiac disease.2
All GSE patients have an increased risk of lymphoma. Symptoms and risk of lymphoma
may be reduced by placing patient on a gluten-free diet.
- Accurate diagnosis of celiac disease requires that patients have gluten
in their diet at the time of testing.
- A diagnosis of celiac disease should not be made on the basis of positive
serological tests alone. Multiple small bowel biopsies from the second part
of the duodenum or beyond are needed to confirm the diagnosis. The only exception
to this rule is if the patient has biopsy-proven dermatitis herpetiformis.
- Antigliadin antibodies are no longer recommended as a routine screening
test because of variable sensitivity and specificity, except in young children
where they may be used as an adjunctive test.
- There is no advantage to using a panel of tests incorporating gliadin,
endomysial, and tissue transglutaminase IgA over a single test detecting either
tissue transglutaminase or endomysial antibodies.
- Detection of tissue transglutaminase antibody or endomysium antibody are
both highly sensitive and specific. However, the tissue transglutaminase antibody
test is more sensitive, easier to perform, and more reproducible. The sensitivity
is 95 percent to 98 percent and the specificity is 94 percent to 95 percent.
- A positive serological test with a small bowel biopsy diagnostic of celiac
disease or skin biopsy-proven dermatitis herpetiformis in a patient with gluten
in his or her diet allows a presumptive diagnosis of celiac disease. A definitive
diagnosis is provided by resolution of symptoms following the introduction
and maintenance of a strictly gluten-free diet.
- When patients successfully maintain a gluten-free diet, tTG IgA antibodies
disappear from serum. Endomysial IgA titers may be ordered, if needed, to
monitor adherence to diet.
- High-risk populations that should be screened for celiac disease include
those with symptoms, individuals with auto immune disorders, (for example,
type 1 diabetes mellitus, thyroid, adrenal, liver, and Sjögren’s
syndrome), and first- and second-degree relatives of patients with celiac
disease. Screening of the general population is not recommended at this time.
- Two percent of patients with celiac disease will be IgA deficient
and unable to make IgA antibodies. These patients need to be screened
using an IgG test. (Reflex
Algorithm.)
- Tests may be ordered separately if you prefer.
- When the diagnosis is uncertain due to indeterminate results, then genetic
markers (HLA DQ typing) may be of benefit.
References
1. Rostom A. Celiac Disease Summary, Evidence Report/Technology Assessment
No. 104. AHRQ Publication No. 04-E029-1, Agency for Healthcare Research and
Quality, June 2004/www.ahrq.gov.
2. Nimmo M. Celiac disease: an update with emphasis on diagnostic considerations.
Laboratory Medicine. 2005; 36(6): 366–369.
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