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What Is the Difference Between a Colonoscopy and a Sigmoidoscopy?

Colorectal cancer screenings can save lives

A woman holds a figure with image of intestines for an article about colonoscopy and colorectal cancer.

Colorectal cancer screenings can save lives

Colorectal cancer is one of the most common cancers in the United States. Not counting skin cancers, it is the third most common cancer in both men and women in the United States.


Colorectal cancer — known also as colon cancer and rectal cancer depending on where it starts — is the third leading cause of cancer death in both men and women. Fortunately, screening tests can detect colon cancer early when treatment is most likely to be successful.


“A screening test can find precancerous polyps in the colon or rectum that can be removed before they turn into cancer,” says Walter Coyle, MD, a gastroenterologist with Scripps MD Anderson Cancer Center and Scripps Clinic. “It can also help find colorectal cancer at an early stage when it is easier to treat and cure.”


In addition to stool tests, there are visual exams used to screen for colorectal cancer. The best known are colonoscopy and sigmoidoscopy.

Colonoscopy vs sigmoidoscopy

Colonoscopy and sigmoidoscopy look at the colon and rectum for any abnormal areas. Both use a thin flexible tube with a camera at the end to look at the colon. They differ in the areas they can see. A colonoscopy uses a longer tube.

What is a colonoscopy?

A colonoscopy examines the entire colon. The colon must be completely clean for this procedure. The day before the test, solid foods must be avoided, and only clear liquids consumed. A solution that makes you go to the bathroom is also taken to make sure there is no waste in your colon.


A colonoscopy is done every 10 years — beginning at age 45 for people with average risk. Sedation is usually needed, meaning someone must drive you home after you wake up.


Colonoscopy is the preferred screening test for colon cancer by multiple organizations and Task Forces including the US Preventive Services Task Force.

What is a sigmoidoscopy?

A flexible sigmoidoscopy is a less invasive screening test that covers only the lower part of the colon. The bowel prep is less complicated. Sedation is usually not needed, and the screening is done every five years.


If a pre-cancerous polyp or cancer is found, you’ll need to have a colonoscopy later to look at the rest of the colon. The test is not widely used for colorectal cancer screening in the US.


Your doctor may recommend a sigmoidoscopy to explore possible causes for abdominal pain, rectal bleeding, changes in bowel habits, chronic diarrhea and other intestinal problems.

Who should get screened?

Screening is recommended from age 45 to 75 years old by the US. Preventive Services Task Force (USPSTF). Additionally, the USPSTF supports screening from 75 to 85 years old if the patient is healthy enough for continued screening. Screening should begin earlier if you have a personal or family history of colorectal cancer or polyps that may become cancer, or an inflammatory bowel disease.

Why is screening so important?

Screening tests works. The number of colorectal cancer cases has been declining for several decades due largely to increased screening. There are more than 1.5 million colorectal cancer survivors in the US.


The decline in colorectal cancer cases has been mainly among adults 50 and older. This is significant because the risk for this type of cancer goes up as you age and is much more common after age 50.


Cases among younger adults has been rising since the mid-1990s, however. About 10.5 percent of new colorectal cancer cases occur in people younger than 50.


Currently, one in three people who should get screened for colorectal cancer has never done so. Reasons vary. Many people are not aware that they need to do a screening. Others are put off by the preparation required.


“However, it is a small price to pay for a procedure that can be life-saving,” Dr. Coyle says.