Stool Tests for Colorectal Cancer
British Columbia Specific Information
You can lower your risk of getting colorectal cancer by getting early colon screening. For information on colorectal screening, including the fecal immunochemical test (FIT) and who should be tested under the new BC Colon Screening program, visit British Columbia Cancer Agency Colon Screening.
For additional information on colon screening, visit Ministry of Health Colorectal Screening for Cancer Prevention in Asymptomatic Patients which also includes the Colorectal Cancer: Guide for Patients. You may also be interested in the Appendix A: Factors Influencing Colorectal Cancer Risk.
Making healthy diet and lifestyle changes can also lower your risk of getting colorectal cancer. For more information, see Healthy Eating Guidelines For Cancer Prevention: Colorectal Cancer. You may also call 8-1-1 to speak with a registered dietitian, Monday to Friday from 9:00 a.m. – 5:00 p.m., or you can Email a HealthLinkBC Dietitian.
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:
- 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.
- Fecal immunochemical test (FIT), also called an immunochemical fecal occult blood test (iFOBT). 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.
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).
Stool tests may be used to check for colorectal cancer, but they are never used to diagnose it. Other tests for colorectal cancer include flexible sigmoidoscopy, colonoscopy, and CT scan (virtual colonoscopy).
A stool test is one of many tests that may be used to screen for colon cancer. Other tests include sigmoidoscopy, colonoscopy, and computed tomographic 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 signs of cancer. FOBT and FIT/iFOBT tests are useful to screen for colon cancer, because tissue or polyps with cancer are more likely to bleed than normal colon tissue. If bleeding is found, more tests will be done to find the cause. It's important to call your doctor if a home test shows blood in your stool. A home test doesn't replace the need for a regular examination by your doctor.
- As part of a routine physical examination for those with a higher chance of getting colorectal cancer, especially from ages 50 to 74.
How To Prepare
Since colorectal cancers do not bleed all the time, FOBT and FIT/iFOBT tests are done over several days on different stool samples. This increases the chance of finding blood in your stool if it exists.
You may need to avoid certain foods for 2 to 3 days before the test. This depends on what kind of stool test you use. If you aren't sure, ask your doctor.
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
You will need to collect stool samples over three different bowel movements on three different days. Be sure to follow the instructions that come with your test kit, including any instructions to avoid certain foods in the days before the test. Return the test card as directed by your health care provider.
If there is blood in your stool, call your doctor as soon as possible.
FIT and iFOBT are two names for the same kind of test.
Instructions are provided by the companies that make the test kits. Each kit is different. Your kit will include a list of steps for you to follow to get accurate results. Return the container with the collected stool sample to any participating laboratory as directed.
The FIT/iFOBT test doesn't require a special diet in the days before you take the test.
How It Feels
You may find it unpleasant to collect a stool sample for these tests.
These tests do not have any risks.
For some FOBT kits, you can read the results yourself. Other tests, including FIT/iFOBT, are read by your doctor.
A normal FIT/iFOBT or FOBT test means that there was no blood in your stool at the time of the test. Normal test results are called negative.
An abnormal FIT/iFOBT or FOBT test means that there was some blood in your stool at the time of the test. Abnormal test results are called positive.
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.
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.
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.
Adaptation Date: 7/13/2016
Adapted By: HealthLink BC
Adaptation Reviewed By: HealthLink BC
Adaptation Date: 7/13/2016
Adapted By: HealthLink BC
Adaptation Reviewed By: HealthLink BC
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