A fecal occult blood test (FOBT) uses a chemical process to measure blood that is hidden (occult) in a patient’s stool. This blood is often present in such small amounts that it can only be detected through chemical testing. The fecal blood test is safe and painless.

Blood in the stool may indicate a number of conditions, but the FOBT is used primarily to detect the presence of growths called polyps in the colon or rectum, or cancer. These conditions cause bleeding, as do other disorders such as inflammatory bowel diseases (including colitis), ulcers and hemorrhoids.

The American Cancer Society (ACS), World Health Organization (WHO) and U.S. Preventive Services Task Force all recommend that people over the age of 50 have an annual FOBT as a part of a routine colorectal exam. In some cases, this test will be performed during the exam in the physician’s office. More often, patients are given a kit to obtain their own sample, which is then returned to the physician or mailed to a laboratory. If blood is discovered during laboratory analysis, additional tests will be needed to locate the source of the bleeding. Such tests will focus on the colon, rectum and upper intestinal tract (including the esophagus, stomach and small bowel).

Despite the recommendation, a 2004 study found that 43 percent of Americans aged 50 and older failed to have a fecal occult blood test or lower endoscopy in the previous year, according to the U.S. Centers for Disease Control and Prevention (CDC). Many patients chose not to have the FOBT because of the nature of the test. However, when the FOBT 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.