Fecal Ocult Blood Test – Understand the Result

The fecal occult blood test (FOBT) is a lab test used to check stool samples for hidden (occult) blood. Occult means hidden. Hidden blood means digestive tract bleeding, which may be an indicator of colon cancer.

Who

Beginning at age 50 FOBT is recommended as part of a routine examination to screen for colon cancer annually.

Based on family history your health provider may recommend this test to you.

Test Samples

Three stool samples are typically collected over several days and prepared on occult blood cards in order to provide for the most effective screening.

Test Preparation

For about three days before the test, your doctor may ask you to avoid certain foods and medications. Follow your doctor’s instructions carefully.

  • Certain fruits and vegetables, including broccoli and turnips
  • Red meat
  • Horseradish
  • Vitamin C supplements
  • Pain relievers, such as aspirin and ibuprofen (Advil, Motrin IB, others)

Result

The fecal occult blood test is normally negative.

For the guaiac-based FOBT, a positive test result indicates that abnormal bleeding is occurring somewhere in the digestive tract. This blood loss could be due to ulcers, diverticulosis, polyps, inflammatory bowel disease, hemorrhoids, blood swallowed due to bleeding gums or nosebleeds, or benign or cancerous tumors.

For the fecal immunochemical test (FIT), a positive result indicates abnormal bleeding in the lower digestive tract. Since this test detects only human hemoglobin, other sources of blood, such as from the diet, do not cause a positive result. Moreover, hemoglobin from bleeding in the upper digestive tract is broken down before it reaches the lower digestive tract and is not detected by the FIT. Thus, the FIT is a more specific test than gFOBT.

A positive result from either the guaiac-based FOBT or immunochemical FIT requires follow-up testing. This usually involves direct imaging of the colon and rectum (sigmoidoscopy or colonoscopy).

 

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