The fecal occult blood test (FOBT) is a diagnostic test to assess for hidden (occult) blood in the stool. . A fecal occult blood test looks for blood in the stool. For your FOBT, you will collect samples of your stool 3 days in a row. This test is commonly used for colorectal cancer. Fecal occult blood testing (FOBT) remains an appropriate screening option for colorectal cancer (CRC). The fecal occult blood test (FOBT) looks for the presence of blood in the feces, which may be a sign of a problem in your digestive system. This increases the chance of finding blood, since the bleeding may not happen every day. , However, FOBT is limited by a lack of patient adherence. Blood in stool may be a sign of hemorrhoids, colorectal cancer, or another condition. If you have certain symptoms, such as abdominal pain, fatigue, pain around your rectum or rectal bleeding, your healthcare provider may. Learn more.