Colorectal cancer screening: when to start and which tests
Key points
- The CDC (US) says most people should begin colorectal cancer screening at age 45.
- The CDC (US) and ODPHP (US) both describe screening for adults aged 45 to 75. For ages 76 to 85, the CDC says the decision is made case by case.
- The CDC (US) says the two stool tests for blood are each done once a year, and a colonoscopy every 10 years for people without a raised risk.
- The CDC (US) lists symptoms, and advises talking to a doctor if you have any of them.
When to start and when to stop
Colorectal cancer is cancer of the colon or rectum. The CDC (US) says most people should begin screening at age 45. It also says the US Preventive Services Task Force recommends screening for adults aged 45 to 75. [1]
ODPHP (US) agrees that people between 45 and 75 should be tested regularly. It adds that you may need to start before 45 if colorectal cancer runs in your family. [2]
For ages 76 to 85, the CDC (US) says the choice to be screened should be made case by case. ODPHP (US) says a doctor may recommend that people in that age range keep getting screened. [1] [2]
Kinds of tests and how often
The CDC (US) describes two stool tests that look for blood in the stool. One is the guaiac-based test, and the other is the FIT, short for fecal immunochemical test. It says each is done once a year. A third stool test, the FIT-DNA test, also looks for changed DNA in the stool, and the CDC says it is done once every 3 years. [1]
The CDC (US) also lists other tests and how often each is repeated. For a flexible sigmoidoscopy, it says to repeat every 5 years, or every 10 years if you also have a FIT every year. For a colonoscopy, it says every 10 years, for people whose risk of colorectal cancer is not raised. For CT colonography, also called a virtual colonoscopy, it says every 5 years. [1]
ODPHP (US) says stool tests are done at home. It says that in general, a stool test means being tested more often. Tests that look inside your colon and rectum mean being tested less often. After an unusual stool test result, ODPHP says the doctor follows up with a colonoscopy, checking for cancer. [2]
What screening looks for
The CDC (US) says colorectal cancer almost always grows from abnormal growths called polyps. Screening can spot polyps, and then they can be taken out before turning into cancer. Screening tests can also find cancer early, when treatment works best. [1]
The CDC (US) says that during a colonoscopy the doctor can find and remove most polyps and some cancers. It also says you could have polyps or colorectal cancer and not have any symptoms. [1] [3]
When to see a doctor
The CDC (US) lists possible symptoms of colorectal cancer. They include blood in or on your stool, a change in bowel habits, belly pain or cramps that do not go away, and weight loss with no known reason. The CDC says that if you have any of these symptoms, talk to your doctor, and that they may be caused by something other than cancer. [3]
The CDC (US) says that if you think you may have an increased risk, you should talk to your doctor. Its examples include inflammatory bowel disease, such as Crohn's disease or ulcerative colitis, and a personal or family history of colorectal cancer or polyps. [1]
The CDC (US) says that people older than 75 should talk to their doctor about screening. ODPHP (US) says to talk with your doctor about your risk, and that a doctor can help you pick the screening test that suits you. [1] [2]
Sources
- CDC (US): Screening for Colorectal Cancer (opens in a new tab). Published June 17, 2026.
- ODPHP (US): Get Tested for Colorectal Cancer (opens in a new tab). Last updated July 7, 2026.
- CDC (US): Symptoms of Colorectal Cancer (opens in a new tab). Published June 17, 2026.
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