How you prepare

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). Your doctor may ask you to avoid certain foods or medicines. 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
• Vitamin C supplements
• Pain relievers, such as aspirin and ibuprofen (Advil, Motrin IB, others)