A test to check for blood in the stool. A brush is used to collect water drops from around the surface of a stool while it is still in the toilet bowl. The samples are then sent to a laboratory, where they are checked for a human blood protein. Blood in the stool may be a sign of colorectal cancer. Also called iFOBT, immunoassay fecal occult blood test, and immunologic fecal occult blood test.