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Fecal occult blood test (FOBT)
A fecal occult blood test (FOBT) is a noninvasive test that detects the presence of hidden (occult) blood in the stool. Such blood may arise from anywhere along the digestive tract. Hidden blood in stool is often the first, and in many cases the only, warning sign that a person has colorectal disease, including colon cancer .
There are two types of FOBTs: 1) the traditional guaiac smear test (Hemoccult, Seracult, Coloscreen), and 2) the newer, flushable reagent pads (EZ DetectT, ColoCARE). They are both useful in detecting hidden blood in the stool, and are mainly used for colorectal cancer screening.
The tests differ in the way they are performed. The flushable reagent pads are available without a prescription at many drugstores. In contrast, the traditional guaiac smear test is completed and interpreted by a medical professional, and these tests are usually available from a laboratory or a doctor's office.
Many consumers prefer the flushable reagent pads because there is no stool handling and no laboratory processing. However, health care providers usually favor the guaiac tests because the large studies that have shown the benefits of colon cancer screening were done with guaiac tests.
How the test is performedSee description under specific type of FOBT.
How to prepare for the testSee description under specific type of FOBT.
How the test will feelSee description under specific type of FOBT.
Why the test is performedThis test is mainly performed for colorectal cancer screening . It may also be performed in the evaluation of anemia .
Normal ValuesA "negative" test result is usual and is normal.
What abnormal results meanPositive test results may indicate the following:
Note that false positives are not uncommon.
Additional conditions under which the test may be performed include the following:
What the risks areA negative test does not necessarily mean there are no colorectal diseases present. Not all polyps bleed, and not all polyps bleed all the time. That is why a FOBT must be used with one of the other more invasive screening measures (sigmoidoscopy, colonoscopy, double barium contrast enema).
Colonoscopy is generally recommended as the preferred follow-up test to a positive FOBT.
Factors that can cause this test to be less accurate include the following:
Drugs that can cause GI bleeding include anticoagulants, aspirin, colchicine, iron supplements in large doses, NSAIDs (anti-inflammatory analgesics), and corticosteroids.
Drugs that can cause false positive measurements include colchicine, iron, oxidizing drugs (for example, iodine, bromides, and boric acid), and reserpine.
Large amounts of vitamin C can cause false-negative results on most FOBTs.
Update Date: 1/12/2003Andrew J. Muir, M.D., M.H.S., Division of Gastroenterology, Duke University Medical Center, Durham, NC. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT