How a stool test can help find colorectal cancer

Colorectal cancer is the second most common cause of cancer death in Canada, yet it is 90% treatable when caught early. Screening for colorectal cancer is easy and convenient. It starts with a stool test that checks your poop (stool) for blood.

Sure, testing poop doesn’t sound like fun. But it could find colorectal cancer early – 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.

Jar for a stool test sample

Stool tests

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.

There are 2 types of stool tests 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 samples at home and place them on a collection card or in a 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.

Jar for a stool test sample

If blood is found in your 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 send you for one of these tests:

a thin, flexible tube with a light and camera at the end looks at the lining of the entire colon.
Flexible sigmoidoscopy
a soft, bendable tube with a light and camera at the end looks at the lining of the rectum and the lower part of the colon.
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
  • inflammatory bowel disease – inflammation of the colon (also called ulcerative colitis or Crohn’s disease)