Blood tests as good as genetic typing for celiac detection
■ Experts say biopsy remains the gold standard for diagnosis, and gene testing still has a role.
By Victoria Stagg Elliott — Posted Sept. 24, 2007
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Combining serologic with genetic testing is not a better strategy for diagnosing celiac disease than either test alone, and intestinal biopsy remains the definitive procedure, according to a study in the Sept. 4 Annals of Internal Medicine.
Combining the use of newer genetic tests with more well-established screening for celiac-related antibodies in the blood has long been discussed as a possibility to improve diagnostic accuracy and reduce the number of people undergoing biopsies. To help settle this debate, researchers at the VU University Medical Center in Amsterdam, the Netherlands, used both modalities on 463 patients referred for biopsy. Sixteen were determined actually to have this condition, but both tests had nearly equal specificity. Using them together was not more accurate.
"If you add genetics to the serology, does it improve the sensitivity? The answer is no. Adding this will not increase the level of confidence in making the diagnosis," said Dr. Alessio Fasano, director of the University of Maryland Center for Celiac Research in Baltimore. He was not affiliated with this study.
Experts complimented the study's elegant design but said it highlighted the challenge of detecting celiac disease, which can have very nonspecific symptoms that mimic many other conditions. It also lacks a conclusive, noninvasive test to diagnose it. Most hold the blood testing in high regard, but it still can miss some patients who go on to have a positive biopsy.
"This is a disease that can really involve any system or organ in your body," said Dr. Fasano, who is also on the Celiac Disease Foundation medical advisory board.
"The serology works extremely well in terms of specificity, but don't rule out celiac just on the basis of a negative test," he said.
Genetic testing is quite sensitive but might label patients as positive because of a genetic predisposition. But, they may never develop the condition. Because of concern about false positives and unnecessarily burdening patients with a gluten-free diet, physicians say they prefer to use this test to determine who among those in high-risk categories, such as family members of people who have it, will not develop this disease. A definitive diagnosis should still be made only with a biopsy.
"Having the gene does not equal having the disease. If you don't have the gene, you probably can't get the disease," said Dr. Joseph Murray, a gastroenterologist and professor of medicine at the Mayo Clinic in Rochester, Minn., who wrote the accompanying editorial.
But although this study was well done, experts said, its conclusions were not groundbreaking. Rather, those who work in this area said the fact that it was published in a primary care journal could mean that it will lead to increased awareness among primary care doctors about this condition. In turn, this attention may help address underdiagnosis, which many view as a more pressing challenge than fine-tuning the diagnostics.
"Celiac is much more common than we ever believed, and it's severely underdiagnosed in this country," said Rima Kittley, MD, a family physician in Lufkin, Texas.
To address this shortcoming, the National Institutes of Health launched a celiac disease awareness campaign in August 2006. Advocates say the serologic testing has made it easier for primary care physicians to screen for this disease, but many hope for even more straightforward, conclusive approaches to make testing more widespread.
"This is a wonderful study that adds to our understanding of testing. But for the significant number of individuals -- both in the U.S. and the rest of the world -- who have celiac and don't know it, it does little to change that fact," said Marla J. Gold, MD, dean of Drexel University's School of Public Health in Philadelphia and a member of the medical advisory board of the National Foundation for Celiac Awareness. "We still need a simple, inexpensive screen."