There is some discomfort associated with both colonoscopy and flexible sigmoidoscopy. Sigmoidoscopy is an office procedure done with a very easy prep and takes only three to five minutes. A total colonoscopy requires a more complete bowel preperation and is done in a hospital or an endoscopy suite as an outpatient. During colonoscopy, sedation is given and the procedure usually takes 15 to 30 minutes. That's a good question.
Sigmoidoscopy does only examine a portion of the colon.
However, about two-thirds of all polyps will be discovered by a sigmoidoscopy. For the average-risk person with no family history of colon cancer or polyps, sigmoidoscopy combined with testing for blood in the stool is a reasonable screening option. If polyps are found on sigmoidoscopy or microscopic blood is found in the stool, a colonoscopy is then done. A barium enema is very accurate for detecting cancer and polyps that are a centimeter in size. For smaller polyps, colonoscopy is better.