GIP and celiac disease: In a longitudinal cohort study conducted in Sheffield, (UK) between 1998 and 2019, patients with established refractory celiac disease (RCD) type 1 and persisting mucosal inflammation and/or ongoing symptoms provided three urine samples for GIP analysis, and 17/36 (47.2%) had at least one positive urinary GIP test, suggesting that gluten exposure may be common in RCD type 1 [135].