Screening Overview

No one looks forward to a colonoscopy, or the bowel prep that goes with it. But colon screening – testing to look for cancer before symptoms start – helps saves lives. Screening can find colon cancer early when it’s small and easier to treat, or even prevent it altogether. Colonoscopy, however, is just one of many tests that can be used to look for colon cancer. And doctors and researchers continue to develop new ones.

Here are several more common tests that can be used to screen for colon cancer. Some are less able to find polyps and more likely to find cancer. Other tests not only can find cancer, but also are better at finding polyps; these tests may be more likely to prevent colon cancer.

Tests that can find polyps and cancer:

Tests that mainly find cancer:

A Colonoscopy uses a flexible lighted tube with a small camera on the end to look at the entire length of the colon and rectum. If polyps are found, they may be removed during the test. To prepare for the test, you may be asked to follow a special diet for a day or two before the test. You will also need to clean out your colon with strong laxatives (called a bowel prep) and sometimes with enemas, as well. Most people are sedated during the test. If nothing is found during the test, you won’t need another one for 10 years.


Flexible sigmoidoscopy is much like colonoscopy, but looks at only part of the colon and rectum. If polyps are found, they may be removed during the test, or you may need to have a colonoscopy later. Bowel prep may be required, but is not as extensive as the one used for colonoscopy. Most people do not need to be sedated during this test. If polyps or suspicious areas are seen, a colonoscopy will be needed to look at the rest of the colon. Flexible sigmoidoscopy must be done every 5 years.


Double-contrast barium enema is a type of x-ray test. It involves putting a liquid called barium into the rectum, which spreads through the colon. Air is then pumped in to spread the barium in a thin, smooth layer to show better detail. Then x-rays are taken. It requires bowel prep, but no sedation. If polyps or suspicious areas are seen on the test, a follow-up colonoscopy will be needed. Barium enemas also need to be repeated every 5 years.


CT colonography (also called virtual colonoscopy) is a scan of the colon and rectum that produces detailed cross-sectional images so the doctor can look for polyps or cancer. It requires bowel prep, but no sedation. Air is pumped into the rectum and colon, and then a CT scanner is used to take images of the colon. If something is seen that may need to be biopsied, a follow-up colonoscopy will be needed. CT colonography must be done every 5 years.

Guaiac-based fecal occult blood test (gFOBT) and fecal immunochemical test (FIT) are used to find tiny amounts of blood in the stool that could be a sign of cancer or large polyps. People take these tests at home with a kit they receive from their doctor’s office, along with instructions. A positive result will need to be followed up with a colonoscopy. However, many times the cause is a non-cancerous condition, such as ulcers or hemorrhoids. Stool tests like these need to be done every year.

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