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Researchers examine prevalence of and testing for celiac disease

Celiac disease (CD) is an inflammatory disorder in which the lining of the small intestine is damaged in response to ingestion of gluten found in wheat, barley, rye, and possibly oats. This disease alters the intestine's ability to absorb nutrients, and it predisposes patients to intestinal lymphoma and a variety of other associated non-intestinal disorders. Although, patients with CD can have diarrhea, weight loss, and other intestinal symptoms, it is becoming increasingly evident that most patients have no symptoms. They are identified instead on the basis of iron deficiency or a number of other associated conditions. CD is effectively treated with a gluten-free diet (GFD) in the vast majority of patients.

Until recently, CD was thought to be a rare disease in the United States. However, a recent systematic review of the evidence revealed that CD is a common medical condition and actually is quite prevalent among certain high-risk groups. The review was conducted by researchers at the University of Ottawa Evidence-based Practice Center, which is supported by the Agency for Healthcare Research and Quality (contract 290-02-0021). Select to access the report and summary, Celiac Disease. Two other Center studies examined the diagnostic accuracy of blood tests for CD and the consequences of such testing. The three studies are described here.

Dube, C., Rostom, A., Sy, R., and others (2005). "The prevalence of celiac disease in average-risk and at-risk Western European populations: A systematic review." Gastroenterology 128, p. S57-S67.

The prevalence of CD in general Western populations is close to 1 percent, but it is somewhat higher in certain Western European populations and much higher in certain high-risk groups, according to this study. For instance, CD affects 3-6 percent of people with type 1 diabetes, up to 20 percent of first-degree relatives of those with CD, 10-15 percent of people who have symptomatic iron-deficiency anemia (IDA), 3-6 percent of those with asymptomatic IDA, and 1-4 percent of individuals who have osteoporosis.

Given the prevalence of the disease, clinicians in a variety of specialties should have a high index of suspicion for the diagnosis of CD, particularly among identified high-risk groups, conclude the researchers. Their findings are based on a systematic review of studies on CD prevalence published from 1966 to December 2003.

Rostom, A., Dube, C., Cranney, A., and others (2005). "The diagnostic accuracy of serologic tests for celiac disease: A systematic review." Gastroenterology 128, pp. S38-S46.

Small bowel biopsy is the historical gold standard for the diagnosis of CD. Recently, several tests that have high sensitivity and specificity for diagnosing CD have become available. The researchers conducted a systematic review of studies published from 1966 to December 2003 on the diagnostic accuracy of these serologic tests for CD.

Endomyseal antibody (EMA) and tissue transglutaminase antibody (tTG) were found to be the highest performing tests. Both of these tests demonstrated a specificity that was over 98 percent in most analyses in adults and children. The specificity of EMA appeared to be slightly higher (close to 100 percent) than that of tTG, but this did not reach statistical significance in the analyses. The sensitivity of both tests was over 95 percent in most analyses. However, the sensitivity of blood tests for CD appears to be lower for patients who do not have intestinal villous atrophy (below 90 percent), which typically defines the disease.

Antigliadin antibody (AGA) was inferior to that of EMA and tTG, and its use should be limited to certain clinical circumstances such as possibly in the diagnosis of young children and monitoring of adherence to a GFD in some patients. Lastly, the authors suggest that in testing of average risk individuals wherein the expected prevalence of CD is close to 1 percent, the positive predictive value of serological testing (that is the chance that a positive test really means the patient has CD) can drop below 90 percent. Since a diagnosis of CD means a lifelong GFD, the authors suggest that a confirmatory biopsy is warranted to avoid inappropriately placing patients on a GFD.

Cranney, A., Rostom, A., Sy, R., and others (2005). "Consequences of testing for celiac disease." Gastroenterology 128, pp. S109-S120.

Recent large screening programs for CD have revealed that two-thirds of those who test positive for the disease have no symptoms. The consequences of testing for CD in symptomatic individuals appears to have a positive impact on patient-relevant outcomes, but the data are less clear for those without symptoms, conclude these researchers. They systematically reviewed studies published from 1990 to December 2003 on the expected consequences of testing for CD in patients with symptoms suggestive of CD, asymptomatic at-risk populations, and the general population.

The review supports the idea that the consequences of testing CD patients who are symptomatic will result in improvements in nutritional status, body mass index, bone mass density, and reduced risk of death and fractures. The data are less clear for those with asymptomatic CD who are identified by screening, especially those with low-grade tissue lesions (on small bowel biopsy) and lower dietary compliance rates. Long-term outcomes have not been extensively studied in those with asymptomatic CD. Although the overall strength of the evidence for this topic was fair to good, the researchers recommend further high-quality studies.

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