In patients with no gastrointestinal problems and no risk factors for colon cancer, the American Cancer Society recommends a first screening colonoscopy at age 50.
However, if you have bowel symptoms such as blood in your stool or a significant change in your bowel movements or their frequency, you should see a doctor right away. If you have any risk factors for colon cancer such as Crohn's disease, ulcerative colitis or a family history of colon cancer, your doctor may want to order the colonoscopy long before you turn 50. If a member of your immediate family, such as a sibling or a parent has had colon cancer, you should begin screening at least 10 years before the age your relative was when diagnosed. The frequency of colonoscopy is determined based on your risk factors and whether or not you have polyps on your colonoscopy. In the average risk patient with a normal colonoscopy the test is repeated every 5-10 years.
Alternatives to colonoscopy include other tests that examine the whole colon such as barium enema or CT colonography (virtual colonoscopy). Less frequently used are the fecal occult blood test cards and sigmoidoscopy. With this method, yearly tests are done to screen your stool for blood. If these tests are negative, a flexible sigmoidoscopy is done every 3-5 years. If the stool blood tests are positive or there are polyps on sigmoidoscopy, a full colon examination is necessary.