Occult Blood  

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 only be detected with the help of chemicals used in a fecal occult blood test. If blood is detected, additional tests may be needed to determine the source of bleeding, because fecal occult blood test can only indicate the presence or absence of blood but not the cause of bleeding.