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.An abnormal or positive FIT result means that there was blood in your stool at the time of the test. . A colon polyp, a pre-cancerous polyp, or cancer can cause a positive stool test. With a positive test, there is a small chance that you have early-stage colorectal cancer.