Fecal occult blood test

The fecal occult blood test (FOBT) is a lab test used to check stool samples for hidden (occult) blood.

Occult blood in the stool may indicate colon cancer or polyps in the colon or rectum — though not all cancers or polyps bleed.

Typically, occult blood is passed in such small amounts that it can be detected only through the chemicals used in a fecal occult blood test.

If blood is detected through a fecal occult blood test, additional tests may be needed to determine the source of the bleeding. The fecal occult blood test can only detect the presence or absence of blood — it doesn't indicate potential sources of bleeding.


Why it's done Risks How you prepare What you can expect Results

Your doctor may recommend a fecal occult blood test to:

  • Screen for colon cancer. If you're age 50 or older and at average risk of colon cancer, your doctor may recommend a fecal occult blood test every year to screen for colon cancer. In addition, however, you may need other screening tests that allow the doctor to examine the colon directly.
  • Evaluate possible causes of unexplained anemia. Anemia is a condition in which there aren't enough healthy red blood cells to carry adequate oxygen to your tissues. Sometimes a fecal occult blood test is used to determine whether bleeding in your digestive tract — such as a bleeding ulcer — is contributing to anemia.
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