What You Should Know About Colorectal Cancer Screening

Colon and rectal cancers may not have symptoms in early stages. Symptoms that do exist, like bowel changes, are generally not very alarming. As a result, these cancers may not be found until later stages, after it has spread to other tissue. This is one factor that has made colorectal cancers a leading cause of cancer deaths. Fortunately, this rate is falling in part due to screening.

Screening tests can find early stage cancer before any symptoms appear. Prompt treatment for early cancer can greatly increase the chance of a cure. It can also prolong your life. These tests can also find abnormal tissue that has a high risk of becoming cancer. Removing it can prevent cancer from starting.

Just talking about colorectal screening can make people a little squeamish. However, its benefits far outweigh the negatives. There are many options and guidelines for screening. Your age, risk factors, and test costs will all play a role in which test is ideal for you. Talk to your doctor about which options may be best for you.

Screening Tests:

Colorectal screening tests are designed to detect cancer or polyps. Polyps are growths on the inside of the colon wall. Most polyps are not cancer. However, most colorectal cancers probably begin as polyps.

Screening options include stool tests and visual exams:

Stool Tests

Stool samples are the least invasive option. A sample of your stool is sent to a lab for testing. Most can be taken at home with a special kit.

Cancer can cause bleeding in the colon or rectum. All the tests look for signs of blood in the stool. However, there are many other conditions that can also cause blood in the stool. Visual tests like the ones listed below will be needed before cancer can be confirmed. Stool test options include:

  • Fecal occult blood test (FOBT)
  • Fecal immunochemical test (FIT)
  • Stool DNA test (FIT-DNA test)—can find blood and altered DNA (cancer or early changes in polyps)

Visual Tests

These tests allow the doctor to see the walls of the rectum and colon. They can spot polyps and other abnormal tissue. It may be used as a screening test or after a positive stool tests to look for causes. Test options include:


A thin tube is inserted into the rectum. It is then slowly passed into the colon. The tube has a small light and camera. It will move through the entire colon until it reaches the small intestine.

The doctor will be able to see polyps and areas of abnormal tissue. The polyps or abnormal tissue can also be removed during this test. The tissue can be sent to a lab to examine for cancer cells.

Flexible Sigmoidoscopy

A thin tube is inserted into the rectum. It is then slowly passed into the lower colon. The tube has a small light and camera.

The doctor will be able to see and remove polyps and areas of abnormal tissue. The polyps or abnormal tissue can also be removed during this test. The tissue can be sent to a lab to examine for cancer cells.

Only the lower part of the colon can be examined. This test does not cover as much of the colon as the colonoscopy does.

CT Colonography

This is a form of x-ray to look for abnormal growth in the colon. Air is passed into the colon to make the images clearer.

A CT scan like this does mean some radiation exposure. If abnormal tissue is found, it cannot be removed during this test. A second procedure will be needed to remove it.

Screening Recommendations

Recommendations can vary. Work with your doctor to find which works best for you. The following are from the American Cancer Society. They are recommended for people with average risk. Average risk is defined as:

  • No history of colorectal cancer, certain types of polyps, or inflammatory bowel disease
  • No family history of colorectal cancer or conditions that increase risk of colon cancer
  • No medical history of radiation to belly or pelvis

People with average risk should start screening at age 45. The screening test may be one of the following:

  • Colonoscopy—every 10 years
  • Flexible sigmoidoscopy—every 5 years
  • CT colonography—every 5 years
  • Fecal occult blood test (FOBT)—every year
  • Fecal immunochemical test (FIT)—every year
  • Stool DNA test—every 3 years

The schedule for people at increased risk may be different. The tests may need to start earlier in life and occur more often. Factors can put you at higher risk include:

  • Personal or family history of colorectal cancer or adenomatous polyps
  • Personal history of chronic inflammatory bowel disease, such as ulcerative colitis or Crohn's disease
  • History of radiation to the belly or pelvis

Talk to your doctor about your test results and schedule. Additional tests may be needed if you had a positive stool test. The time to your next test may also change based on your results. For example, if polyps were found your doctor may recommend more frequent screening.

What Tests Do You Need?

Talk to your doctor about your risk factors for colorectal cancer. Then ask about screening tests. There are benefits and risks to each type of test. Knowing all the information will help you make the best screening choice for you.


American Cancer Society
National Cancer Institute


Canadian Cancer Society


Colorectal cancer screening. EBSCO DynaMed Plus website. Available at: https://www.dyname.... Updated May 21, 2018. Accessed Ju;y 10, 2018.
Colorectal cancer screening—patient version. National Cancer Institute website. Available at https://www.cancer.gov/types/colorectal/hp/colorectal-screening-pdq. Update February 23, 2018. Accessed Ju;y 10, 2018.
Colorectal cancer screening tests. American Cancer Society website. Available at: https://www.cancer.org/cancer/colon-rectal-cancer/detection-diagnosis-staging/acs-recommendations.html. Updated May 30, 2018. Accessed July 10, 2018.
Colorectal (colon) cancer. Centers for Disease Control and Prevention website. Available at
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Updated June 20, 2018. Accessed July 10, 2018.
Last reviewed March 2017 by Michael Woods, MD
Last Updated: 7/10/2018

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