The fecal occult blood (FOB) test is 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 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.