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What is a fecal occult blood test?

Dr. Donald Petroski, MD
Gastroenterologist

The fecal occult blood test (FOBT) is a screening test for colon cancer that checks for tiny amounts of blood in feces that cannot be seen. Guaiac FOBT (gFOBT) testing requires multiple stool samples to be collected by a person using a kit, which is then returned to the doctor. No colon cleansing is necessary.

Yearly testing is recommended if FOBT is the only screening test performed. False-positive test results are possible with FOBT. Additional procedures, such as colonoscopy, may be needed if the test result shows blood in the stool.

FIT (fecal immunochemical test or iFOBT) also detects blood via a stool sample but is more accurately than FOBT in finding precancerous polyps or colorectal cancers. A small amount of blood leaks into the colon and is detected upon sampling. It's easy to do, done in the privacy of the home and not affected by diet or medicines since it only detects human blood. It is more accurate than the FOBT, inexpensive and covered by Medicare insurance. But it must be done annually.

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The fecal occult blood test (FOBT) is used to find occult (hidden) blood in feces. The idea behind this test is that blood vessels at the surface of larger colorectal polyps or cancers are often fragile and easily damaged by the passage of feces. The damaged vessels usually release a small amount of blood into the feces, but only rarely is there enough bleeding to be visible in the stool.

The FOBT detects blood in the stool through a chemical reaction. This test cannot tell whether the blood is from the colon or from other parts of the digestive tract (such as the stomach). If this test is positive, a colonoscopy is needed to see if there is a cancer, polyp or other cause of bleeding such as ulcers, hemorrhoids, diverticulosis (tiny pouches that form at weak spots in the colon wall) or inflammatory bowel disease (colitis).

This screening test is done with a kit that you can use in the privacy of your own home. An FOBT done during a digital rectal exam in the doctor's office is not sufficient for screening. In order to be beneficial the test must be repeated every year.

People having this test will receive a kit with instructions from their doctor's office or clinic. The kit will explain how to take a stool or feces sample at home (usually specimens from 3 consecutive bowel movements that are smeared onto small squares of paper). The kit should then be returned to the doctor's office or medical lab (usually within 2 weeks) for testing.

A fecal occult blood test checks for hidden (occult) blood in the stool. It involves placing a very small amount of stool on a special card, which is then tested in the physician's office or sent to a laboratory.

Healthcare providers may suggest a fecal occult blood test (FOBT) for colorectal cancer screening. An FOBT is recommended for people at risk for colorectal cancer every year. In this test, doctors check for hidden blood in three consecutive stool samples.

A fecal occult blood test (FOBT) is used to find small amounts of hidden (occult) blood in the stool. A sample of stool is tested for traces of blood. People having this test will receive a kit with instructions that explain how to take stool samples at home. The kit is then sent to a lab for testing. If the test is positive, further tests will be done to pinpoint the exact cause of the bleeding. A rectal exam in the doctor's office may examine for occult blood, but this is NOT considered adequate for colorectal cancer screening. The test should only be done with a take-home kit.

A newer kind of stool blood test is known as FIT (fecal immunochemical test). It is like the FOBT, perhaps even easier to do, and it gives fewer false positive results. The test is simple, cost effective and done at home (patient must retrieve samples of stool from the toilet bowl). It must be done yearly and is considered the least effective means of detecting cancer. All positive results must be evaluated with a colonoscopy.

The fecal occult blood test (FOBT) is a stool sample that is analyzed for blood. Occult means it is not visible, but is measurable chemically. So, this is blood you would not see but may be dissolved in the stool. FOBT is a screening test, but a weak one, as bleeding from a tumor can be intermittent.

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