Overview

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 can't determine what's causing the bleeding.

A fecal occult blood test isn't recommended if you have colon cancer symptoms. If you notice blood in your stool or in the toilet or if you experience abdominal pain or a change in your bowel habits, make an appointment with your doctor.