Stool Tests for Colorectal Cancer
For some FOBT kits, you can read the results yourself. Other tests, including FIT/iFOBT and stool DNA, are read by your
A normal FIT/iFOBT or FOBT test means that there was no blood in your stool at the time of the test.
A normal sDNA test means that no abnormal cells were found. 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.
An abnormal sDNA test means that some abnormal cells were found. Abnormal test results are called positive.
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.
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 early-stage 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
- Having cleaning products in the toilet water at the time of the test.
What To Think About
- 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.
- The stool DNA test is still new, and it isn't available everywhere.
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Helfand M (2009). Adult preventive health care. In EG Nabel, ed., ACP Medicine, Clinical Essentials, chap. 10. Hamilton, ON: BC Decker.
Hoffman RM, et al. (2010). Colorectal cancer screening adherence is higher with fecal immunochemical tests than guaiac-based fecal occult blood tests: A randomized, controlled trial. Preventive Medicine, 50(5–6): 297–299.
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.