Colorectal Cancer: Screening

Screening means checking for cancer before a person has symptoms. Regular screening is very important for colorectal cancer because it can often find cancer early, when it is likely to be easier to treat. In fact, screening can even prevent many colorectal cancers. That’s because screening lets the healthcare provider find and remove growths inside the colon or rectum (colorectal polyps) before they have a chance to turn into cancer. 

Types of screening tests

Several tests can be used to screen for colorectal cancer. Some of these tests can also find colorectal polyps.

Screening tests to find colorectal polyps and cancer

  • Colonoscopy. This test looks at your rectum and your entire colon. It uses a colonoscope, which is a long, lighted tube with a small video camera on the end. The provider inserts the scope into your rectum and up into your colon. The provider looks for polyps or other abnormal areas. These can be removed and sent to a lab for testing. This test usually requires sedation, where you are given medicine to make you sleepy during the test. A colonoscopy is the only test that lets the provider see the entire colon and rectum, and remove pieces of any abnormal areas for testing. If you have any of the other tests and something uncertain is found, you will likely need a colonoscopy. 

  • Flexible sigmoidoscopy. This test looks at your rectum and the lower part of your colon. Your healthcare provider inserts a thin, lighted tube with a small video camera on the end into your rectum. The tube is called a sigmoidoscope. He or she looks for polyps or other abnormal areas. These can be removed and sent to a lab for testing.

  • Virtual colonoscopy (CT colonography). This test is a special type of CT scan of the colon and rectum. Once the CT images are taken, a computer combines them to create a 3-D picture. This lets the provider look for polyps or cancer.  

Screening tests to find cancer only

These tests look for signs of cancer in your stool or feces. These tests can be done at home. But they are less likely to find polyps. And they must be done more often than the tests above.

  • Fecal occult blood test (FOBT) or fecal immunochemical test (FIT). These tests look for hidden or occult blood in the stool. Blood vessels in cancers and sometimes in polyps are easily broken during a bowel movement. This may cause blood to show up in your stool. For these tests, you collect a small amount of your stool with a brush or wooden applicator. Then you smear it on a special card that can find blood. In most cases you need to do this for a few bowel movements in a row. You then send the cards to your provider’s office or to a lab.

  • Stool DNA test. This test looks for DNA changes in cells in the stool that might be signs of cancer. It also looks for hidden blood in stool. For this test, you collect an entire bowel movement. This is done using a special container put in the toilet. The sample is sent to a lab for testing. 

What expert groups recommend

The American Cancer Society and U.S. Preventive Services Task Force advise people at average risk for colorectal cancer start screening at age 45. This is because of an increase of colorectal cancer in people younger than age 50. How often you need these screening tests depends on which test you have.

Screening for those who are age 45 and of average risk for colorectal cancer includes:

  • A colonoscopy every 10 years, or

  • A flexible sigmoidoscopy every 5 years (or every 10 years with yearly FIT stool test), or

  • A CT colonography (virtual colonoscopy) every 5 years, or

  • A fecal occult blood test (FOBT) or fecal immunochemical test (FIT) every year

  • A stool DNA test every 1 to 3 years

Regular colorectal cancer screening for those at average risk continues through the age 75 for people in good health and a life expectancy of 10 years or more. For people ages 76 to 85, talk with your healthcare provider about continued screening. Screening for people older than 85 is not advised.

Average vs. high risk

Most people are at average risk and should follow advice like those listed above. But some people are at higher risk for colorectal cancer based on things like:

  • A personal or family history of colorectal cancer

  • Certain kinds of polyps

  • They have or might have certain inherited syndromes, such as familial adenomatous polyposis (FAP), and Lynch syndrome or hereditary non-polyposis colon cancer (HNPCC)

  • A personal history of inflammatory bowel disease such as Crohn's or ulcerative colitis

  • They were treated with radiation to the belly (abdomen) or pelvis in the past

These people might need to start screening at a younger age. They also may need to be screened more often. For instance, if certain types of polyps are found on your colonoscopy, you may need to get another colonoscopy in the next 3 years instead of waiting 10 years.

Talk with your healthcare provider

It's important to know your risk. Talk with your provider about your risk for colorectal cancer, when you should start screening, and which tests might be right for you. Also talk with your health insurance carrier to know which tests are covered by your insurance.

If you have a test other than a colonoscopy and have an abnormal test result, you will need to have a colonoscopy. This is so that tissue can be taken out and checked for cancer.

Online Medical Reviewer: Jessica Gotwals RN BSN MPH
Online Medical Reviewer: Sabrina Felson MD
Online Medical Reviewer: Todd Gersten MD
Date Last Reviewed: 1/1/2023
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