A fecal occult blood test is a test for blood in the feces or stool. The word occult means hidden, so a fecal occult blood test is sometimes used as a screen for colon cancer when there are no symptoms in place. However, a positive result does not necessarily mean that cancer is present, just that there is blood in the digestive system somewhere. Other reasons for a positive test might include an ulcer. When there is a positive result of a fecal occult blood test, this would show that further investigation should be carried out to find the cause of the bleeding.