What Is the Difference Between a Colonoscopy and a Sigmoidoscopy?

Choosing the colon cancer screening that’s right for you

Physician and patient discussing difference between a colonoscopy and a sigmoidoscopy

Choosing the colon cancer screening that’s right for you

Colon cancer is one of the most common cancers diagnosed in men and women in the United States and most often occurs among people 50 and older. It is the number two cause of cancer death in both men and women.


A screening exam can find precancerous polyps that can be removed before they turn into cancer. 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 two main procedures to screen for colorectal cancer — colonoscopy and flexible sigmoidoscopy.


What’s the difference?

Comparing a colonoscopy and a sigmoidoscopy

Colonoscopy and sigmoidoscopy are screening tests that use a thin flexible tube with a camera at the end to look at the colon but differ in the areas they can see. A colonoscopy examines the entire colon, while a sigmoidoscopy covers only the lower part of the colon, also known as the rectum and sigmoid colon.


A sigmoidoscopy is a less invasive screening test. The bowel prep is less complicated. Sedation is usually not needed and the screening is done every five years. A colonoscopy is done every 10 years and sedation is usually needed, meaning someone has to drive you home after you wake up.


Since a sigmoidoscopy only looks at part of the colon any cancers or polyps farther into the colon cannot be detected. 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.


But sometimes only the rectum and sigmoid colon need close inspection.


Your doctor may recommend a flexible sigmoidoscopy exam to explore possible causes for abdominal pain, rectal bleeding, changes in bowel habits, chronic diarrhea and other intestinal problems. The procedure allows your doctor to check for inflammation, ulcers, abnormal tissue, polyps or cancer.

Getting screening is most important

While significant improvements have been made to prevent colorectal cancer, only about 60 percent of the people in the U.S. who should be screened for colorectal cancer actually have the test.


“Many may be put off by the preparation required. However, it is a small price to pay for a procedure that can be life-saving," said Walter Coyle, MD, head of gastroenterology at Scripps Clinic.


"According to the American College of Gastroenterology cancer risk is reduced by 90 percent following a colonoscopy and the removal of precancerous polyps,” Dr. Coyle said.


Screening should begin at age 50 unless you have a family history of colon cancer, in which case it should begin earlier. Check with your health provider to determine which test is best for you. But the most important thing is to get tested.


Thanks to medical advances in prevention, early detection and treatment, there are now more than 1 million survivors of colorectal cancer, according to the American Cancer Society.


“It’s not something most people want to talk about, but by age 50, you should have a conversation with your doctor about colorectal cancer,” Dr. Coyle said.