<qa>  What is the gold standard of duodenal biopsy?The aim of this study is to assess the clinical utility of the whole blood transglutaminase-based rapid test against current serological tests and the gold standard of duodenal biopsy. The investigators will recruit patients n1000 from the endoscopy department at the Royal Hallamshire Hospital, Sheffield, United Kingdom UK. The patients recruited for this study will already have been referred for a consultation and gastroscopy. In addition, these patients will already have been serologically tested for IgA TTG, EMA and a total IgA immunoglobulin level as per normal clinical practice. 