What are screening tests for colorectal cancer?

Screening tests are used to find cancers before they are large enough to cause any warning signs. Because finding cancer early means that you're more likely to be cured, it is important for you to have appropriate screening tests. Your doctor will choose the tests that are right for you. The following are some screening tests for colorectal cancer:

Digital Rectal Exam. In this exam, your doctor puts his or her gloved finger into your rectum to find any growths. This exam is simple to do and is not painful. However, because this exam can find less than 10% of colorectal cancers, it must be used along with another screening test.

Fecal Occult Blood Test. In this test, your stool is checked for blood that you can't see. Your doctor gives you a test kit and instructions to use at home. Then you return a stool sample to your doctor for testing. If blood is found, another test is done to look for a polyp, a cancer or another cause of bleeding.

Many things that you eat can make this test turn out positive even though you don't really have blood in your stool. This is called a "false-positive" test. These things include some raw vegetables, horseradish, rare red meat, iron supplements and aspirin. Don't eat these things for 2 days before you have a fecal occult blood test. Some medical conditions, like hemorrhoids, can also cause a false-positive test result.

Flexible Sigmoidoscopy. In this test, your doctor puts a thin, flexible, hollow tube with a light on the end into your rectum. The tube is connected to a tiny video camera so the doctor can look at the rectum and the lower part of your colon.

This test can be a bit uncomfortable, but it lets your doctor see polyps when they are very small (before they can be found with a fecal occult blood test). Because flexible sigmoidoscopy may miss cancerous polyps that are in the upper part of the colon, some doctors prefer a screening test called colonoscopy. Your doctor will discuss these options with you.

Double-Contrast Barium Enema. For this test, you are given an enema (injection of fluid into the rectum) with a liquid that makes your colon show up on an x-ray. Your doctor looks at the x-ray to find abnormal spots in your entire colon. If you have an abnormal spot, you are then examined by colonoscopy.

Colonoscopy. Before you have this test, you are given a medicine to make you relaxed and sleepy. A thin, flexible tube connected to a video camera is put into your rectum, and the doctor looks at your whole colon. The tube can also be used to remove polyps and cancers during the exam. Colonoscopy may be uncomfortable, but it is usually not painful.

When should I be screened for colorectal cancer?

Colorectal cancer is more common in older people, so doctors usually screen people 50 years of age and older. Some people have risk factors that make them more likely to get colorectal cancer at a young age. Screening should begin earlier in these people.

You should begin screening at a younger age if any of the following are true about you:

  • Have had colorectal cancer or large polyps in the past
  • Have a close relative (brother, sister, parent or child) who has had colorectal cancer before age 60
  • Have ulcerative colitis or Crohn's disease
  • Have a hereditary colon cancer syndrome

If you are in one of these groups, you may also need to be tested more often than a person who doesn't have risk factors for colorectal cancer.

Any one of the following screening programs (with a digital rectal exam at each screening) may be used, beginning at 50 years of age:

  • Fecal occult blood testing every year
  • Flexible sigmoidoscopy every 5 years
  • Fecal occult blood testing every year plus flexible sigmoidoscopy every 5 years
  • Double-contrast barium enema every 5 years
  • Colonoscopy every 10 years
The American Academy of Family Physicians believes that any of these tests or combinations of tests can be a good screening method. The American Cancer Society and the American Gastroenterological Association have similar guidelines.

Talk to your family doctor to decide which screening tests you should have and how often you should be screened. If you don't have any risk factors for colorectal cancer, you will probably have your first screening test around 50 years of age.