Fecal occult blood testing (FOBT) remains an appropriate screening option for colorectal cancer (CRC). For your FOBT, you will collect samples of your stool 3 days in a row. If you have certain symptoms, such as abdominal pain, fatigue, pain around your rectum or rectal bleeding, your healthcare provider may. A fecal occult blood test looks for blood in the stool. , However, FOBT is limited by a lack of patient adherence. 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. . Blood in stool may be a sign of hemorrhoids, colorectal cancer, or another condition. The fecal occult blood test (FOBT) is a diagnostic test to assess for hidden (occult) blood in the stool. This test is commonly used for colorectal cancer. Learn more.