Test Overview

A stool test is one of many tests used to look for colorectal cancer. These tests may find cancer early, when treatment works better. Colorectal cancer affects the large intestine (colon) and the rectum.

There are two kinds of stool tests used in Canada. The specific test used depends on the guidelines in your province.

    • Fecal immunochemical test (FIT). This is a test that may be easier to do at home than FOBT. There are no drug or food restrictions, and collecting a stool sample may take less effort. This test should be done every one to two years from ages 50 to 74.
    • Fecal occult blood test (FOBT). For this test, you put tiny samples of your stool on a special card or cloth and send it to a lab. The lab uses chemicals to find blood that you can't see with the naked eye. This test should be done every one to two years from ages 50 to 74.

Blood in the stool may be the only symptom of colorectal cancer, but not all blood in the stool is caused by cancer. Other conditions that can cause blood in the stool include:

  • Hemorrhoids. These are enlarged, swollen veins in the anus. Hemorrhoids can form inside the anus (internal hemorrhoids) or outside of the anus (external hemorrhoids).
  • Anal fissures. These are thin tears in the tissue that lines the anus (anal sphincter) up into the anal canal.
  • Colon polyps. These growths of tissue are attached to the colon and often look like a stem or stalk with a round top.
  • Peptic ulcers. These sores form when the digestive juices made in the stomach eat away at the lining of the digestive tract.
  • Ulcerative colitis. This type of inflammatory bowel disease (IBD) causes inflammation and sores (ulcers) in the inner lining of the colon and rectum.
  • Gastroesophageal reflux disease (GERD). This is the abnormal backflow (reflux) of food, stomach acid, and other digestive juices into the esophagus.
  • Crohn's disease. This type of inflammatory bowel disease causes inflammation and ulcers that may affect the deep layers of the lining of the digestive tract.
  • Use of aspirin or non-steroidal anti-inflammatory drugs (NSAIDs).

A stool test is one of many tests that may be used to screen for colon cancer. Other tests include sigmoidoscopy, colonoscopy, and CT colonography. Which screening test you choose depends on your risk, your preference, your doctor, and what tests are available in your area. Some tests may not be covered under your provincial health care plan. Talk to your doctor about what puts you at risk and what test is best for you.

Why It Is Done

Stool tests are done to look for blood in the stool, since tissue or polyps with cancer are more likely to bleed than normal colon tissue. If blood is found, more tests will be done to find the cause.

How To Prepare

Since colorectal cancers do not bleed all the time, some stool tests may be done over several days on different stool samples. This increases the chance of finding blood in your stool if it exists. The instructions that come with the home test kit will tell you whether to take one sample or several samples over several days.

With the FOBT, you will be given instructions about foods to avoid in the days before the test. Some medicines may also need to be stopped for a brief time before the test.

Do not do the stool tests during your menstrual period or if you have active bleeding from hemorrhoids. Also, do not test a stool sample that has been in contact with toilet bowl cleaning products, including those that turn the water blue.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form (What is a PDF document?).

How It Is Done

Fecal immunochemical test (FIT)

The test kit contains the things you need to collect small samples of stool. For some types of FIT, you may need to collect a stool sample on 2 or more days.

The FIT test doesn't require a special diet in the days before you take the test.

When the test is done, follow the instructions to return the test. Some tests provide the results right away. If your test shows that blood was found, call your doctor as soon as possible.

Fecal occult blood test (FOBT)

The test kit contains the things you'll need, such as test cards or a special test pad. You may need to collect stool samples over three different bowel movements on three different days. Be sure to follow any instructions about foods or medicines to avoid in the days before the test.

Your instructions may say to:

  • Put tiny samples of stool onto paper cards. Return all the samples right after you collect the last sample.
  • Place a special test pad in the toilet after having a bowel movement. The pad will change colour if the stool has blood in it.

If there is blood in your stool, call your doctor as soon as possible.

How It Feels

You may find it unpleasant to collect a stool sample for these tests.

Risks

There is no risk from the stool test itself. For this test, you put a sample of stool on a card or you collect a stool sample. Or you may collect the entire stool.

But there are some important things to think about. If your test is positive, you will need to have a colonoscopy. This would be used to see if the stool test result is from colorectal cancer. But blood in the stool is more often caused by something other than cancer. These other causes could include hemorrhoids, ulcers, or taking aspirin. A positive test result could lead you to worry. And you might have a colonoscopy that you didn't need.

Results

If your test sample is sent to a lab or returned to your doctor's office, your test results will likely be read by your doctor. Some labs may send you the results. And depending on the type of test you choose, you may be able to see the results after completing the last step.

Stool tests
Normal:

A normal FIT or FOBT test means that there was no blood in your stool at the time of the test. Normal test results are called negative.

Abnormal:

An abnormal FIT or FOBT test means that there was some blood in your stool at the time of the test. Abnormal test results are called positive.

Normal results

If a stool test is normal, it does not always mean colorectal cancer or colon polyps are not present. That's because these tests can miss polyps and some cancers.

Talk with your doctor about how often you should do a test, depending on your age and any risk factors you may have for colorectal cancer.

Abnormal results

A colon polyp, a precancerous polyp, or cancer can cause a positive stool test. With a positive test, there is a small chance that you have colorectal cancer.

Talk with your doctor about what test you may need next. Most of the time, an abnormal stool test means that you will need to have a colonoscopy.

What Affects the Test

Reasons you may not be able to have a stool test or why the results may not be helpful include:

  • Having blood in the urine, menstrual bleeding, hemorrhoids, an anal fissure, bleeding gums, or nosebleeds.
  • Having cleaning products in the toilet water at the time of the test.

What To Think About

Some tests for colorectal cancer screening may not be available in all areas. Check with your doctor to find out what tests are used in your area.

  • Stool tests can produce false-positive and false-negative results.
    • False-positive means that the test may be positive when you don't have a polyp or cancer.
    • False-negative means that the test may be negative when you do have a polyp or cancer.
  • These tests may miss polyps and some cancers.

References

Other Works Consulted

  • Haas JS (2013). Adult preventive health care. In EG Nabel, ed., ACP Medicine, section 2, chap. 2. Hamilton, ON: BC Decker.
  • Leddin D, et al. (2010). Canadian Association of Gastroenterology position statement on screening individuals at average risk for developing colorectal cancer: 2010. Canadian Journal of Gastroenterology, 24(12): 705-714. Also available online: http://www.cag-acg.org/position-statements.
  • Levin B, et al. (2008). Screening and surveillance for the early detection of colorectal cancer and adenomatous polyps, 2008: A joint guideline from the American Cancer Society, the U.S. Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. CA: A Cancer Journal for Clinicians, 58(3): 130-160.
  • Nadel MR, et al. (2005). A national survey of primary care physician's methods for screening for fecal occult blood. Annals of Internal Medicine, 142(2): 86-94.
  • Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.

Credits

Adaptation Date: 12/3/2017

Adapted By: HealthLink BC

Adaptation Reviewed By: HealthLink BC

Adaptation Date: 12/3/2017

Adapted By: HealthLink BC

Adaptation Reviewed By: HealthLink BC