- Intestinal biopsies: Endoscopy and gastrointestinal biopsy will be done only if there is evidence of malabsorption. Some of the biopsy tissue may be kept for research. Patients are pre-medicated to allay anxiety, but are fully conscious during the procedure. A flexible tube is inserted into the stomach or small intestine through the mouth. The tube allows the doctor to see the intestinal mucosa and to project the image onto a TV screen. At various places in the mucosal surface, small pieces of tissue are plucked out using a small space at the tip of the endoscope. The procedure takes 30 to 60 minutes.