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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
There are three kinds of stool tests:
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:
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
CT scan (virtual colonoscopy).
Many tests may be used to screen for colon cancer. Which screening test you choose depends on your risk, your preference, and your doctor. Talk to your doctor about what puts you at risk and what test is best for you.
information on tests for colorectal cancer, see:
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Stool tests are done:
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. A stool DNA test requires only one sample.
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 that turn the water
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
medical test information form(What is a PDF document?).
You will need to collect stool samples over three different bowel movements on three different days. The test kit includes a wooden applicator and test cards. 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.
Other ways to do FOBT:
If there is blood in your stool, call your doctor as soon as possible.
You will need to collect two stool samples for testing over different days. The test kit includes brushes and test cards. Be sure to follow the instructions provided in the test kit. The FIT/iFOBT test doesn't require a special diet in the days before you take the test.
You will receive a kit from your doctor with supplies and instructions for doing this test at home. Always follow the instructions in your kit.
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 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.
Reasons you may not be able to
have a stool test or why the results may not be helpful include:
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.
December 7, 2011
Adam Husney, MD - Family Medicine & Arvydas D. Vanagunas, MD - Gastroenterology
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