Diagnosis of Celiac Disease
The Agency for Healthcare Research and Quality has released an evidence report on celiac disease. “Celiac Disease” is available online athttp://www.ahrq.gov/clinic/epc-sums/celiacsum.htm.
Celiac disease represents a spectrum of clinical features. Although “classic” celiac disease (i.e., fully developed, gluten-induced villous atrophy and classic features of intestinal malabsorption) is most commonly described, it appears that most patients have atypical disease (i.e., fully developed gluten-induced villous atrophy in the setting of another disorder such as iron deficiency, osteoporosis, short stature, or infertility). The prevalence of celiac disease is difficult to estimate, but a recent study found rates of approximately 1 percent in the general population and 4.5 percent in high-risk groups, such as first-degree relatives of persons with the disease.
The diagnosis classically is made on the basis of clinical suspicion—recognizing atypical presentations such as isolated iron deficiency, combined iron and folate deficiency, and osteoporosis—compatible with a duodenal biopsy in persons with a gluten-containing diet, followed by clinical and histologic improvement when a gluten-free diet is started. However, several serologic markers are available that have altered the classic diagnostic pathway. IgA antigliadin antibodies (AGA), IgA anti-endomysial antibodies (EMA), and anti-tissue transglutaminase antibodies (tTG) have high sensitivity and specificity in diagnosing celiac disease. However, AGA antibody testing in children and adults has a limited role, and the reported diagnostic parameters for EMA and tTG antibody testing are taken from studies in which the prevalence of celiac disease was much higher than that seen in usual clinical practice. The positive predictive values reported for these tests will not be as high as those reported when these tests are used to screen the general population.
Human leukocyte antigen DQ2/DQ8 testing appears to be useful in the diagnosis of celiac disease. The test has high sensitivity (i.e., 90 to 95 percent). However, approximately 30 percent of the general population and an even higher proportion of high-risk persons also carry these markers, so the specificity of this test is not ideal. Its greatest diagnostic use appears to be its negative predictive value, making it useful when negative at ruling out disease.
Testing for celiac disease in at-risk and symptomatic patients is associated with good outcomes. These patients appear to be more compliant with a gluten-free diet and would be expected to benefit from this intervention. The data are less clear for asymptomatic screen-identified patients. Outcomes in these patients have not been studied extensively, but compliance with a gluten-free diet appears problematic, particularly in patients diagnosed in adulthood.