Screening for colon cancer can find cancer at an early curable stage and can prevent cancer by finding and removing polyps that might eventually turn into cancer.

Colorectal cancer is more common in older people, so doctors usually screen people 50 years of age and older.

Doctors generally advise screening at a younger age for people who have risk factors that make them more likely to get colorectal cancer. You should be screened for colorectal cancer before age 50 if 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, such as familial adenomatous polyposis or hereditary non-polyposis colorectal cancer.

If you are in a high-risk group for colorectal cancer, you may also need to be tested more often than someone who doesn't have risk factors.

Screening Tests for Colorectal Cancer
Several tests, which are generally accepted by members of the medical community, are available to screen for colorectal cancer. Some are used alone, while others are used in combination with each other. Your doctor can talk with you about which type of test is best for you. These tests include:

• Fecal occult blood test (FOBT). This test checks for occult (hidden) blood in the stool. You receive a test kit from your doctor or health care provider. At home, you place a small amount of your stool from three bowel movements in a row on test cards. You return the cards to your doctor's office or a lab, where the stool samples are tested for hidden blood.
• Flexible sigmoidoscopy. This test allows the doctor to examine the lining of your rectum and lower part of your colon using a thin, flexible, lighted tube called a sigmoidoscope. It is inserted into your rectum and lower part of the colon.  
• Combination of FOBT and flexible sigmoidoscopy. Some experts recommend combining the two tests described above to increase the chance of finding polyps and cancers.
• Colonoscopy. This test – considered by many medical professionals to be the "gold standard" of screening exams for colorectal cancer – is similar to flexible sigmoidoscopy except that it allows the doctor to examine the lining of your rectum and entire colon using a thin, flexible, lighted tube called a colonoscope. While you are under sedation, this tube is inserted into your rectum and colon to enable the doctor to find and remove most polyps and some cancers.
• Double Contrast Barium Enema. This test allows the doctor to see an x-ray image of the rectum and entire colon. First you receive an enema with a liquid called barium that flows from a tube into the colon, followed by an air enema. The barium and air create an outline around your colon, allowing the doctor to see if abnormalities are present.
• Other tests. Computerized tomography (CT or CAT) colonography (also referred to as "virtual colonoscopy") and fecal DNA tests are experimental screening tests that are still under development. CT colonography is offered in some health care settings, but you should be aware that it is still considered experimental and should be used only in the context of a clinical trial. These exams are not accepted as standard practice at the present time.  Learn more about experiment screening tests for colorectal cancer from the Cancer Research and Prevention Foundation.

Colorectal Cancer Screening Guidelines
The American Cancer Society, the American Academy of Family Physicians, and the American Gastroenterological Association all have similar guidelines for colorectal cancer screening. Each believes that any of the tests or combinations of tests listed above may be used (together with a digital rectal exam at each screening). For people who have no risk factors, colorectal screening should begin at 50 years of age and continue with:

• Fecal occult blood testing every year
• Flexible sigmoidoscopy every five years
• Fecal occult blood testing every year plus flexible sigmoidoscopy every five years
• Double-contrast barium enema every 5  years
• Colonoscopy every 10 years

Your family physician can advise you on which screening tests you should have and how often you should be screened.