Fecal Occult Blood Test (FOBT)

How To Prepare

Since colorectal cancers do not bleed all the time, the test for blood in the stool is done over several days on three different stool samples. This increases the chance of finding blood in your stool.

Before doing a fecal occult blood test (FOBT), avoid the following for 2 to 3 days before the test.

• Turnips, beets, radishes, horseradish, artichokes, mushrooms, broccoli, bean sprouts, cauliflower, apples, oranges, bananas, grapes, and melon. These foods can cause the test to be positive for blood when blood is not in the stool (false-positive test results).
• Red meat, which may cause false test results. Small amounts of chicken, turkey, or fish will not affect the test.
• Iron supplements
• ASA (or products that contain ASA) and non-steroidal anti-inflammatory drugs (NSAIDs) or other medicines that irritate the stomach or intestines
• Vitamin C supplements

Do not do the test 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 blue.

Talk to your health professional 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?).

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Author:	Douglas Dana Jan Nissl, RN, BS	Last Updated: October 23, 2006
Medical Review:	Adam Husney, MD - Family Medicine Kathleen Romito, MD - Family Medicine Jerome B. Simon, MD, FRCPC, FACP - Gastroenterology
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