FLEXIBLE SIGMOIDOSCOPY OR COLONOSCOPY? Narrated by James. Why might you need a flexible sigmoidoscopy rather than a colonoscopy? Flexible sigmoidoscopy looks at your rectum and sigmoid colon. Sometimes it reaches the descending colon too. Enemas clear this lower section of bowel. It is a shorter test, with light sedation or none. Colonoscopy aims to examine your whole colon, so it needs full bowel preparation. The shorter test can investigate rectal bleeding in selected patients, or check known inflammation in the lower bowel. Problems further up may need a colonoscopy. Follow your provided instructions.