A fecal occult blood test (FOBT) is an analysis of a person’s stool that can reveal blood that is hidden (occult) in feces. It is typically performed by having the patient obtain stool samples at home and sending them into a laboratory for analysis. The FOBT is used to detect polyps or cancer in the colon or rectum. A polyp is a noncancerous (nonmalignant) growth that protrudes from the inner wall of the colon or rectum. It can develop into cancer if left untreated.

Blood vessels in the surface of colorectal polyps, adenomas and cancers are often fragile. The passage of feces through the colon and rectum frequently damages these vessels, releasing blood into the feces. However, it is rare for the bleeding to be so severe that the blood becomes visible in stool.

FOBT detects this hidden (occult) blood through a chemical reaction, but the test cannot determine where the blood originated. If blood is detected, further tests will be necessary to identify the source of the bleeding. In addition to polyps and cancer, the detected bleeding can occur from anywhere in the body - from the mouth to the anus - and can stem from conditions such as:

• Ulcers
  
• Hemorrhoids. Masses or clumps of tissues within the anal canal.
  
• Diverticulosis. Tiny pouches that form at weak spots in the colon wall.
  
• Inflammatory bowel disease (colitis)
  
• Crohn’s disease and ulcerative colitis. Chronic inflammatory diseases of the intestines.

When this test is performed every one to two years in patients ages 50 to 80, it reduces the number of deaths from colorectal cancer by up to 30 percent, according to the National Cancer Institute (NCI). The American Cancer Society (ACS) and other organizations recommend that people over the age of 50 have an annual FOBT as a part of a routine colorectal examination. However, compliance rates generally do not match that recommendation. The U.S. Centers for Disease Control and Prevention reports that in 2004, 57 percent of Americans aged 50 or older reported having had a fecal occult blood test or lower endoscopy within the previous year.


Although the screening rates for colorectal cancer are beginning to increase, the CDC estimates that 41.8 million people aged 50 and older have not been screened according to recommended guidelines.

Like all cancer tests, fecal occult blood tests have advantages and disadvantages. These include: