Fecal occult blood testing, or FOBT, is a test used to screen for colorectal cancer. A sample of stool is collected from the patient and tested for blood.
The purpose of the test is to look for occult blood in the stool, which is blood that isn’t visible to the naked eye. Unlike bright red blood that is seen from hemorrhoids, occult blood in the stool can indicate inflammation, infection, bleeding from polyps or, possibly cancer. If blood is detected during the test, follow-up testing such as colonoscopy will be conducted to determine the reason for blood in the stool.
FOBT is often negative in patients with colon cancer, meaning no blood shows up in that specific test sample. For this reason, FOBT must be done along with flexible sigmoidoscopy. It is also important to note that a positive FOBT doesn't necessarily mean that cancer is present. A positive FOBT can also indicate things like infection, inflammation, or bleeding polyps, without cancer. Many providers now rely on the fecal immunohistochemical test, called FIT, to detect blood in the stool.