Fecal occult blood test (FOBT)

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Fecal occult blood test

Stool occult blood test

A negative test does not necessarily mean there are no colorectal diseases present. Not all polyps bleed, and not all polyps bleed all the time. That is why a FOBT must be used with one of the other more invasive screening measures (sigmoidoscopy, colonoscopy, double barium contrast enema).

Colonoscopy is generally recommended as the preferred follow-up test to a positive FOBT.

Factors that can cause this test to be less accurate include the following:

• Bleeding gums following a dental procedure
• Eating red meat within 3 days of the test
• Eating turnips or horseradish

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Drugs that can cause GI bleeding include anticoagulants, aspirin, colchicine, iron supplements in large doses, NSAIDs (anti-inflammatory analgesics), and corticosteroids.

Drugs that can cause false positive measurements include colchicine, iron, oxidizing drugs (for example, iodine, bromides, and boric acid), and reserpine.

Large amounts of vitamin C can cause false-negative results on most FOBTs.

In general, avoiding food is not recommended, with the exception of red meat as described above.

Review Date: 03/08/2008
Reviewed By: Christian Stone, MD, Division of Gastroenterology, Washington University in St. Louis School of Medicine, St. Louis, MO. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org).