A recent study adds additional nuance to the interpretation of celiac serology (Clin Gastroenterol Hepatol 2013; 11: 398-403).
In this study the authors analyzed anti-TTG IgA levels from 104 consecutive pediatric and adult patients who were not IgA deficient. The study took place between 2000-2009. In addition, samples from 537 consecutive controls were available for comparison.
The study determined the likelihood of having celiac disease based on antibody level from four different companies and pre-test clinical factors. The general population pretest probability was 1%; the pretest probability for their population was 6% if their were gastrointestinal complaints, 14% if weight loss/small stature was present, 11% for patients with anemia/iron deficiency, and 9% for patients with malabsorption.
Even in those with high antibody titers (>10-fold normal), if they were asymptomatic, only 53%-75% had celiac disease (depending on the individual assay). That is, >10-fold elevation with some commercial assays did not correspond to >10-fold elevation in all of the assays leading to variable probabilities.
In patients with low level elevations (1-3 fold times the cut-off level), the probability of having celiac disease in asymptomatic individuals varied from 1% to 7%. Thus, mild elevations in TTG IgA are not highly predictive in this asymptomatic population. However, in those with pretest probability of 14%, the frequency of celiac disease varied among the four assays from 14% to 56%.
Take home message: Not all assays for celiac disease are comparable. While very high serology levels (>10 fold) are associated with celiac disease, in asymptomatic patients as few as 53% may have celiac disease.
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