This is not Medical advice: The biopsy determination of celiac disease requires demonstration of the abnormalities in the proximal small intestine. It is not possible to get such a biopsy going through the anus. The colonoscope does not reach that far. The biopsy instrument must go through the mouth. This is usually achieved with a upper endoscopy (AKA gastroscopy, EGD) A colonoscopy is frequently preformed for the investigation of diarrhea but does not and can not detect celiac disease. Joseph A. Murray, MD.

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