Screening for colorectal cancer is easy and convenient.
A stool test might be something you’d rather avoid. But it could save your life – it’s that simple. Colorectal cancer responds best to treatment when it is found and treated early. Treatment is most effective before the disease spreads outside of the colon.
If you are aged 50 to 74 and not at high risk for colorectal cancer, have a stool test every 2 years.
If you are 75 or older, talk to your doctor about whether a stool test is right for you.
There is convincing evidence that stool tests with appropriate follow-up can significantly reduce deaths from colorectal cancer.
Follow-up for a positive test should include a colonoscopy or double contrast barium enema (an x-ray of the large intestine) or flexible sigmoidoscopy.
A colonoscopy is not usually recommended as a routine screening test for people who don’t have a high risk for colorectal cancer. There isn’t enough evidence that it is more helpful than other available tests, and it has a slightly greater risk for harm.
If you are at high risk for colorectal cancer
People at high risk for colorectal cancer may need to be tested more often and at an earlier age than people with average risk. You may be at higher risk if you have:
- a parent, sibling or child who has had colorectal cancer
- a personal history of colorectal cancer or polyps
- inflammatory bowel disease
- some inherited syndromes
- signs or symptoms of colorectal cancer
Talk to your doctor about your risk. If you are at higher than average risk, you may need a personal plan for testing.
Polyps or tumours in the colon have blood vessels that can release a small amount of blood onto the stool when it passes by. Stool tests check for this hidden (occult) blood, which you can’t see with your eyes.
Two types of stool tests are used in Canada to screen for colorectal cancer.
Guaiac-based fecal occult blood test (gFOBT)
Uses a chemical reaction on a paper card to find traces of blood in the stool.
Fecal immunochemical test (FIT)
Uses specific antibodies to find traces of blood in the stool.
For both types of test, you collect the stool samples at home and place them on a stool collection card or in a stool collection container. Depending on where you live, you then take or mail the samples to a medical lab. Certain foods and drugs can affect some stool tests, so be sure to follow the instructions that come with the test kit. Ask your doctor if you have any questions.
If there is blood in the stool
If a stool test shows traces of blood in your stool, you will need to have more tests to find out where the bleeding is coming from and why. Your doctor may suggest:
- Colonoscopy – A thin, flexible tube with a light and camera at the end is used to look at the lining of the entire colon. Watch a colonoscopy.
- Flexible sigmoidoscopy – A soft, bendable tube with a light and camera at the end is used to look at the lining of the rectum and the lower part of the colon.
- Double-contrast barium enema – An x-ray of the colon and rectum that uses a special dye (called barium). The dye helps show the lining of the colon more clearly.
If the tests show something abnormal, tissue samples for further testing (a biopsy) may be taken during a colonoscopy or sigmoidoscopy.
Other reasons for having blood in the stool
Having blood in your stool doesn’t always mean that you have polyps or cancer. Blood may come from the colon or from other parts of the digestive tract, such as the stomach or anus. The bleeding can be caused by:
- ulcers – sores on the lining of your digestive tract
- hemorrhoids – enlarged or swollen veins of the anus and rectum
- diverticulosis – tiny pouches that form at weak spots in the colon wall
- ulcerative colitis or Crohn’s disease – inflammation of the colon, also often called inflammatory bowel disease
Benefits and risks of colorectal cancer screening
Almost every test or procedure has benefits and risks. It’s important to be aware of them so that you can make an informed decision that’s right for you. No screening test is 100% accurate, but the scientific evidence tells us that having stool tests leads to a decrease in death rates in people with cancer.
- Better survival rates – In most cases, the earlier a cancer is found (detected), the better your chance of survival. Research has shown that people who have regular stool tests are more likely to survive colorectal cancer. Stool tests check for hidden blood found in the stool. Polyps or tumours in the colon have blood vessels on their surface that can release a small amount of blood in the stool. Stool tests can prevent cancer by detecting polyps that can be removed before they become cancerous.
- Better quality of life – Early detection may also mean less treatment and less time spent recovering.
- False-positive results – This happens when test results suggest cancer even though cancer is not present. False positives can cause anxiety, stress and possibly painful and unnecessary tests to rule out cancer (that is, to make sure you don’t have cancer when the screening test has suggested you might).
- False-negative results – This happens when cancer is not detected by the test even though it is present. False negatives can cause you or your physician to ignore other symptoms that suggest the presence of cancer, causing a delay in diagnosis and treatment.
- Overdiagnosis – Certain cancers may never cause any symptoms or decrease life expectancy or quality of life. However, research shows that most colorectal cancers are harmful and that colorectal cancer should be found and treated as early as possible.
- Increased exposure to harmful procedures – A colonoscopy may be needed after a positive stool test. There can be risks with this procedure such as bleeding and bowel perforation.