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. Also known as colon cancer and rectal cancer depending on where it starts, colorectal cancer 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 at Scripps Clinic. “It can also help find colorectal cancer at an early stage when it is easier to treat and cure.”

The U.S. Preventive Service Task Force and American Cancer Society recommend screening for colorectal cancer starting at age 45 for people at average risk. Both stool-based tests or visual exams are recommended screening tests for colorectal cancer. If you are 45 or older, talk to your doctor about which is right for you.

There are several screening test options. The best known visual exams are colonoscopy and sigmoidoscopy.

Colonoscopy vs sigmoidoscopy

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

What is a colonoscopy?

A colonoscopy uses a long flexible tube called a colonoscope and examines the entire colon.

The procedure is recommended every 10 years. Sedation is usually needed, meaning someone must drive you home after you wake up.

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.

What is a sigmoidoscopy?

A flexible sigmoidoscopy is a less invasive procedure that looks at less than half of the colon and rectum. 

The bowel prep is less complicated. Sedation is usually not needed, and the screening is done every five years.

Sigmoidoscopy is not widely used for colorectal cancer screening in the U.S. 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.

If a pre-cancerous polyp or cancer is found during a sigmoidoscopy, it should be followed up with a colonoscopy.

Colorectal cancer screening by age

Most cases of colorectal cancer are diagnosed in adults 65 to 74 years of age. Cases among younger adults have been rising since the mid-1990s, however. About 10.5% of new colorectal cancer cases occur in people younger than 50.

Medical experts recommend regular colorectal cancer screening for people at average risk starting at age 45 through the age of 75.

Screening for people ages 76 through 85 should be based on their preferences, life expectancy, overall health and prior screening history.

Screening may begin before age 45 for people at increased or high risk of colorectal cancer. This includes people with:

  • A family history or personal history of colorectal cancer or certain types of polyps
  • A personal history of inflammatory bowel disease
  • A family history of a hereditary colorectal cancer syndrome
  • A personal history of radiation to the abdomen or pelvic area to treat a prior cancer

Why is screening so important?

Screening tests work. 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 U.S.

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.

Raising awareness about screening

Currently, about 70% of adults are up to date with colorectal cancer screening, according to the Centers for Disease Control and Prevention.

Many people are still not aware that they need to do a screening or at what age. 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.

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