NEW YORK (Reuters Health) – Challenging biopsied duodenal mucosa with gliadin, the toxic fraction of the gluten of wheat, can help establish a final diagnosis of celiac disease in cases in which sensitivity to gluten is suspected but unconfirmed by standard diagnostic tests, report researchers from Italy. In vitro gliadin challenge is particularly helpful in those started on a gluten-free diet before having a proper diagnosis, Dr. Carolina Ciacci, from University of Salerno, told Reuters Health. “People often start the gluten-free diet before diagnosis, just to see if they feel better (often doctors give that wrong advice),” she explained in an email. Often in these cases, “they need to return on a gluten-containing diet, wait for months sometimes having symptoms, and repeat blood tests and endoscopy to disclose the presence of celiac disease.” The current study shows that “gluten can be put directly on a biopsy; the biopsy of a person with celiac disease develops inflammation markers upon gluten contact. There is no need to eat it.” In the presence of gliadin, the intestinal mucosa of patients with celiac disease undergoes several modifications that can partly be reproduced in vitro, the investigators explain in a report online September 27 in the American Journal of Gastroenterology. They evaluated in vitro gliadin challenge in 337 adults visiting a tertiary center for food intolerance and celiac disease. The cohort consisted of 57 patients without celiac disease (negative controls), 221 patients with celiac disease (positive controls; 166 untreated and 55 on a gluten-free diet) and 59 “difficult diagnosis” patients. The difficult diagnosis group consisted of patients with suspected celiac disease in whom diagnosis could not be made because the diagnostic work-up was initiated while on treatment with gluten-free diet and/or of non-concordant diagnostic tests. Using duodenal samples collected from all patients, the researchers measured gliadin-induced mucosal expression of seven inflammatory markers: PY11265, ICAM-1 (intercellular cell adhesion molecule), HLA-DR, CD3, CD25, CD69, and transglutaminase 2 IgA. HLA-DR had the highest accuracy for celiac disease in analyses on negative controls and positive controls (also excluding patients on a gluten-free diet). The area under the receiver operating curve was 0.99. The accuracy of the test did not increase when this marker was combined with any of the other markers. The findings were similar in a subgroup of 39 patients in the “difficult diagnosis” group who agreed to go off a gluten-free diet after gliadin challenge for reassessment of celiac disease-specific antibodies. The findings for HLA-DR, the researchers point out, were consistent at incubation times of 3 hours and 24 hours, in the absence and in the presence of treatment with gluten-free diet, and in patients with difficult diagnosis. How many people fall into this “difficult diagnosis” category? “Many, many, but nobody knows exactly how many,” Dr. Ciacci told Reuters Health. The investigators note in their paper that this test could provide a psychological boost for patients who don’t have celiac disease but are afraid to return to a normal gluten-containing diet. Dr. Ciacci cautioned, however, that to perform in vitro gliadin challenge “you need an endoscopy unit next to a good laboratory equipped for cell culture. We suggest the test be performed only in celiac disease/food intolerance centers.” Reuters Health asked Dr. Daniel Leffler, director of clinical research, The Celiac Center at Beth Israel Deaconess Medical Center, Boston, for his thoughts on the study. He said “improvements in diagnosis of celiac disease in people on a gluten free diet are greatly needed.” “This is a well designed and performed study,” Dr. Leffler added; “however the techniques used, namely HLA-DR expression in cultured duodenal biopsies, is probably too complicated to be done in routine clinical use and will be limited to specialized research centers.” Reference: In Vitro Gliadin Challenge: Diagnostic Accuracy and Utility for the Difficult Diagnosis of Celiac Disease Am J Gastroenterol 2011