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By Mayo Clinic staffVarious foods, dietary supplements and medications can affect the results of a fecal occult blood test — either indicating that blood is present when it isn't (false-positive) or missing the presence of blood that's actually there (false-negative). To ensure accurate test results, follow your doctor's instructions carefully.
For about three days before the test, your doctor may ask you to avoid:
- Certain fruits and vegetables, including broccoli and turnips
- Red meat
- Horseradish
- Vitamin C supplements
- Aspirin
- Nonsteroidal anti-inflammatory drugs, such as ibuprofen (Advil, Motrin, others)
- Levin B, et al. Screening and surveillance for the early detection of colorectal cancer and adenomatous polyps, 2008: A joint guideline from the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. Gastroenterology. 2008;134:1570.
- Hundt S, et al. Comparative evaluation of immunochemical fecal occult blood tests for colorectal adenoma detection. Annals of Internal Medicine. 2009;150:162.
- Fecal occult blood test: The test sample. American Association for Clinical Chemistry. http://www.labtestsonline.org/understanding/analytes/fecal_occult_blood/sample.html. Accessed March 12, 2009.
- Fecal occult blood test: The test. American Association for Clinical Chemistry. http://www.labtestsonline.org/understanding/analytes/fecal_occult_blood/test.html. Accessed March 12, 2009.
- Bynum TE. Evaluation of occult gastrointestinal bleeding. http://www.uptodate.com/home/index.html. Accessed March 12, 2009.
- Pignone M, et al. Meta-analysis of dietary restriction during fecal occult blood testing. Effective Clinical Practice. 2001;4:150.
- Van Rossum LG, et al. Random comparison of guaiac and immunochemical fecal occult blood tests for colorectal cancer in a screening population. Gastroenterology. 2008;135:82.
