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Dec/Jan 2010 Issue
Celiac Disease Testing Matters
Patients are usually screened for celiac disease with a blood panel. The diagnosis is then confirmed with a biopsy of the small bowel. Not every case of celiac disease is a straightforward diagnosis, in part because each test for celiac has an important limitation.
Doctors screen with a panel of blood tests since each test alone can vary in terms of specificity and sensitivity.
• Anti-tissue transglutaminase (tTG) antibodies
• Endomysial antibodies (EMA)
• IgG tissue transglutaminase
• Total IgA antibodies
Limitations: Blood tests require the patient be on a regular (gluten-containing) diet in order to be accurate. Tests may need to be repeated over time as normal results don’t exclude the possibility the disease will develop later in life.
The small bowel biopsy is currently the gold standard for diagnosing celiac disease. Doctors examine a small tissue sample, obtained via endoscopy, for evidence of flattened villi, the hair-like projections in the small intestine that absorb nutrients.
Limitations: The biopsy, which requires the patient be on a regular (gluten-containing) diet in order to be accurate, may miss the portion of the small intestine with flattened villi. Because celiac disease doesn’t cause uniform intestinal damage, experts recommend that four to six different samples be taken from the third part of the duodenum. A biopsy may need to be repeated over time as normal results don’t exclude the possibility the disease will develop later in life.
Using a small sample of blood, cheek or saliva, the genetic test looks for two markers associated with celiac disease, HLA-DQ2 and HLA-DQ8.
Limitation: The genetic test only rules out celiac disease. A positive test result does not indicate the patient has or will develop celiac disease.
A skin biopsy is the gold standard for diagnosing dermatitis herpetiformis (DH), an uncomfortable skin condition associated with celiac disease. It’s characterized by an itchy, blistering rash, often on the elbows and knees. Treatment for DH is strict adherence to the gluten-free diet.
Limitations: The skin biopsy must be performed on uninvolved skin adjacent to the affected area since the inflammatory reaction interferes with immunological testing. Blood tests and intestinal biopsy do not always accurately diagnose celiac disease in patients who have DH.