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.Tests for fecal occult blood detect blood

in the stool that is not visible on gross inspection, usually less than 50 mg of hemoglobin per

gram of stool. Normal adults usually show less than 2 to 3 mg/gm.