Colonoscopy vs Sigmoidoscopy: What's the Difference?

The Main Difference

A colonoscopy examines the entire colon, all the way to where it meets the small intestine. A sigmoidoscopy examines only the lower third of the colon, the rectum and the sigmoid colon. Both use a flexible camera, but they reach different distances.

Colonoscopy in Brief

A colonoscopy is the gold standard for colon cancer screening because it sees the whole colon and lets me remove polyps in the same exam. It requires full bowel prep and sedation. A normal result usually means you do not need another for several years.

Sigmoidoscopy in Brief

A flexible sigmoidoscopy looks only at the lower colon. The prep is simpler, and it is often done with little or no sedation. It is useful for evaluating specific lower-colon symptoms like rectal bleeding, but because it does not see the upper colon, it can miss problems higher up.

Comparing the Two

• How much is seen: colonoscopy views the entire colon, sigmoidoscopy only the lower third.
• Prep and sedation: colonoscopy needs full prep and sedation, sigmoidoscopy needs less of both.
• Polyp removal: both can remove polyps in the area they reach, but only colonoscopy covers the whole colon.
• Best use: colonoscopy for complete screening and prevention, sigmoidoscopy for focused evaluation of lower-colon symptoms.

Which One Do You Need?

For routine colon cancer screening, colonoscopy is usually preferred because it checks the entire colon and can prevent cancer by removing polyps. Sigmoidoscopy has a role for certain targeted questions or when a limited exam is appropriate. Dr. Khan will recommend the right test based on your age, symptoms, and history.

The Takeaway

Both tests are safe and valuable, and the difference comes down to how much of the colon is examined. If you are due for screening or have lower digestive symptoms, we can help you decide which exam fits your situation. Compare the screening options in our colonoscopy vs Cologuard guide.