How you prepare

By Mayo Clinic Staff

Various foods, dietary supplements and medications can affect the results of some fecal occult blood tests — 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
  • Pain relievers, such as aspirin, ibuprofen (Advil, Motrin, others)
Jun. 18, 2011