Last week we talked about the proposed new guidelines for colorectal cancer screening from the U.S. Preventive Services Task Force (USPSTF), which recommend that screening start at age 45 rather than 50. We talked about some of the reasons why the recommendation is changing, including the fact that about 12% of colorectal cancers are now diagnosed in people under 50. Today we’ll talk about some of the ways to screen for colorectal cancer.
What screening tests are done for colorectal cancer?
There are two types of screening tests for colorectal cancer that are recommended by the USPSTF. Direct visualization tests involve looking directly at the colon and rectum to look for abnormal findings. Stool-based tests check the stool for signs of cancer.
Stool-based tests include:
Fecal immunochemical test (FIT) – This test looks for tiny amounts of blood in the stool.
Guaiac-based fecal occult blood test – This test also looks for hidden blood in the stool through a chemical reaction.
Stool DNA test – This test looks for hidden blood and abnormal sections of DNA that could be from cancer.
Direct visualization tests include:
Colonoscopy – A doctor uses a colonoscope (a flexible tube with a light and video camera on the end) to look at the entire length of the rectum and colon. If the doctor sees anything abnormal or concerning, instruments can go through the tube to take a biopsy of the abnormal area.
Flexible sigmoidoscopy – This is similar to a colonoscopy, but only examines the rectum, the portion of the colon called the sigmoid colon, and most of the colon on the left side of the abdomen. This is a little over 1/3 of the amount examined with a colonoscopy.
CT colonography – This is a special type of CT (Cat) scan, which is used to look for abnormal areas within the colon and rectum.
How are these tests used?
There are specific screening recommendations regarding which tests to do and how often these tests should be done, depending on your own risk for developing colorectal cancer, as well as your own health and other factors. Your risk for colorectal cancer depends on things such as your family history, and other factors. A flexible sigmoidoscopy needs to be done more often than a colonoscopy because it sees less of the colon. However, it requires less preparation to clean out the bowel, has less risk of complications, and can often be done without anesthetic. These factors may make it preferred in certain individuals.
Sometimes a combination of tests is recommended. For instance, a person at average risk for colorectal cancer may do a flexible sigmoidoscopy every 10 years and have the FIT every 2 years in between. Some people will have the FIT or guaiac fecal occult blood test done every two years, without having a colonoscopy or sigmoidoscopy. If there are abnormal findings, then a colonoscopy would be done to investigate the abnormal findings.
Which test is right for you and how often it should be done is something that you should discuss with your family doctor (or GI doctor if you have one). Your doctor will discuss your family history, and any risk factors that you may have, along with your own medical history and make a recommendation. You can then discuss with your doctor the risks and benefits regarding the recommendations and make an informed decision about which test (or tests) is best for you.
As I mentioned last week, we should keep in mind that screening recommendations do not apply to patients who have symptoms that might be caused by colorectal cancer. In a patient with symptoms, your doctor will recommend tests for the purposes of investigating your symptoms. These recommendations may be different than those used for screening.
Any person with persistent symptoms that might be caused by colorectal cancer (which can include rectal bleeding, change in bowel habits, persistent abdominal pain, or pelvic pain), should have these symptoms investigated with appropriate diagnostic tests, even if they are young and have no family history of colorectal cancer.
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Dr. Anita Bennett MD – Health Tip Content Editor