DefinitionA colonoscopy is an internal examination of the colon (large intestine) and rectum, using an instrument called a colonoscope.How the test is performedThe colonoscope has a small camera attached to a flexible tube. Unlike sigmoidoscopy, which can only reach the lower third of the colon, colonoscopy examines the entire length of the colon.You will lie on your left side with your knees drawn up toward the chest. After you have received a sedative and pain reliever, the colonoscope is inserted through the anus and gently advanced to the lowest part of the small bowel.Air will be inserted through the scope to provide a better view. Suction may be used to remove fluid or stool.Because the health care provider gets a better view as the colonoscope is pulled back out, a more careful exam