Fecal Occult Blood Test (FOBT)

Results

A fecal occult blood test finds blood in the stool by placing a small sample of stool on a chemically treated card, pad, or wipe. Then a special chemical solution is put on top of the sample. If the card, pad, or cloth turns blue, there is blood in the stool sample.

You can read the results for some FOBT kits. Other tests are read by your health professional.

Fecal occult blood test

Normal:	A normal test (no color change) means that there was no blood in your stool at the time of the test. Normal test results are called negative.
Abnormal:	An abnormal test (blue color change) means that there was some blood in your stool at the time of the test. Abnormal test results are called positive.

Normal results

If the test does not find blood in your stool, that does not mean colorectal cancer or colon polyps are not present (false-negative). FOBT is positive in 30% to 50% of the people who have colorectal cancer. Talk with your health professional about how often you should do a test depending on your age and any risk factors you may have for colorectal cancer.

Abnormal results

If the test finds blood in your stool, it does not always mean you have cancer (false-positive). An FOBT has a high rate of false-positive results. This can occur because the blood comes from another source, such as from red meat you have eaten, menstrual bleeding, hemorrhoids, Crohn's disease, ulcerative colitis, a stomach ulcer, the use of aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs), and many other causes.

A colon polyp, a precancerous polyp, or cancer can cause a positive test. With a positive test, there is about a 5% to 10% chance that you have early-stage colorectal cancer. No cause is found for about 50% of tests that show blood in the stool, so it is not clear why the test was positive.

If blood is found in your stool, talk with your doctor about what test you may need next.

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Author:	Jan Nissl, RN, BS	Last Updated: September 1, 2006
Medical Review:	Kathleen Romito, MD - Family Medicine Jerome B. Simon, MD, FRCPC, FACP - Gastroenterology
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