The Harvard Medical School Family Health Guide
Diagnostic Tests - Fecal Occult Blood Test
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How do I prepare for the test?

  • If the traditional test is used, you collect samples of your stool at home and send them to a laboratory or clinic for analysis.Your doctor gives you a kit with all of the materials you need.A newer test uses flushable pads to detect blood in the toilet bowl following a bowel movement, so that no stool samples are required.

    For several days before taking the samples, you must avoid medicines that can interfere with the results. These include NSAIDs and blood thinners (see "Medication precautions," page 35) which can cause minor stomach bleeding, thereby giving an abnormal test result. If you have hemorrhoids, wait until they stop bleeding before doing the test. Women shouldn't collect stool samples near the time of menstruation. Finally, avoid using toilet bowl cleaners for several days before the test, because these chemicals can affect the results if they come in contact with your stool sample.

    For several days before the test, you also need to avoid foods and vitamins that can affect the test result. Foods to avoid include red meat (the blood it contains can turn your test positive), radishes, turnips, cabbage, cauliflower, horseradish, uncooked broccoli, and cantaloupe (all of which contain a chemical that can turn the test positive), and citrus fruits and vitamin C supplements (which can turn the test falsely negative).

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