Real-World Gluten Exposure in Patients With Celiac Disease on Gluten-Free Diets, Determined From Gliadin Immunogenic Peptides in Urine and Fecal Samples

It is not clear how often patients who are on gluten-free diets (GFDs) for treatment of celiac disease still are exposed to gluten. We studied levels of gluten immunogenic peptides (GIP) in fecal and urine samples, collected over 4 weeks, from patients with celiac disease on a long-term GFD. We performed a prospective study of 53 adults with celiac disease who had been on a GFD for more than 2 years (median duration, 8 y; interquartile range, 5–12 y) in Argentina. At baseline, symptoms were assessed by the celiac symptom index questionnaire. Patients collected stool each Friday and Saturday and urine samples each Sunday for 4 weeks. We used a commercial enzyme-linked immunosorbent assay to measure GIP in stool and point-of-care tests to measure GIP in urine samples. Overall, 159 of 420 stool and urine samples (37.9%) were positive for GIP; 88.7% of patients had at least 1 fecal or urine sample that was positive for GIP (median, 3 excretions). On weekends (urine samples), 69.8% of patients excreted GIP at least once, compared with 62.3% during weekdays (stool). The number of patients with a sample that was positive for GIP increased over the 4-week study period (urine samples in week 1 vs week 4: P < .05). Patients with symptoms had more weeks in which GIP was detected in stool than patients without symptoms (P < .05). The number of samples that were positive for GIP correlated with titers of deamidated gliadin peptide IgA in patients’ blood samples, but not with levels of tissue transglutaminase. Patients with celiac disease on a long-term GFD still frequently are exposed to gluten. Assays to detect GIP in stool and urine might be used to assist dietitians in assessment of GFD compliance.