What is a fecal occult blood test?
Fecal occult blood testing (FOBT) is testing that is performed on samples of stool in order to detect occult blood (blood that is not visible to the naked eye) in otherwise normal-colored stool. Fecal occult blood usually is a result of slow (often intermittent) bleeding from inside the upper or lower gastrointestinal tract. The slow bleed does not change the color of the stool or result in visible bright red blood. Therefore, the blood is found only by testing the stool for blood in the laboratory. Occult bleeding has many of the same causes as other forms of more rapid gastrointestinal bleeding, such as rectal bleeding (passage of red blood and/or blood clots rectally) and melena (black tarry stool as a result of bleeding from the upper intestines such as ulcers). Please read the Rectal Bleeding article for a more detailed explanation of different patterns of gastrointestinal bleeding.
Why is fecal occult blood testing done?
A fecal occult blood test is done primarily to detect colon cancer in people without intestinal symptoms. Cancers of the colon are common and frequently produce fecal occult blood long before they cause other symptoms such as abdominal pain, rectal bleeding, or changes in bowel habits. In addition, some precursors of colon cancer, specifically, some types of colon polyps, also may bleed slowly and cause fecal occult blood. By finding the cancers early through fecal occult blood testing when the cancers are small and before they metastasize (spread to distant organs), patients may be cured of their cancers by removing them surgically. By removing precancerous polyps that are found through fecal occult blood testing, cancer may be prevented.
How is a fecal blood test performed?
For fecal occult blood testing, several (usually three) samples of stool are collected for testing. The reason for testing multiple samples is that bleeding from cancers and polyps often is intermittent and only one of the samples may show blood.
There are two types of fecal occult blood testing, 1) chemical and 2) immunologic.
How do the results of chemical fecal occult blood testing compare with immunologic fecal occult blood testing?
A chemical fecal occult blood test is inexpensive and easy, but it has several disadvantages.
The immunologic fecal occult blood test has additional advantages over the chemical fecal occult blood test. First, it is more sensitive for blood. This means that given the same amount of blood in the stool, the immunologic fecal occult blood test will more frequently be abnormal. In other words, it will more frequently detect cancers and precancerous polyps. Second, it is more specific for blood. That is, there will be fewer abnormal tests due to interfering substances in the diet, and as a result, an abnormal immunologic fecal occult blood test will more commonly be due to cancer or a precancerous polyp. As a result, less follow-up testing (for example, colonoscopy) will be necessary to pursue a falsely abnormal fecal occult blood test.
How is a fecal blood test performed?
For fecal occult blood testing, several (usually three) samples of stool are collected for testing. The reason for testing multiple samples is that bleeding from cancers and polyps often is intermittent and only one of the samples may show blood.
There are two types of fecal occult blood testing, 1) chemical and 2) immunologic.
How do the results of chemical fecal occult blood testing compare with immunologic fecal occult blood testing?
A chemical fecal occult blood test is inexpensive and easy, but it has several disadvantages.
The immunologic fecal occult blood test has additional advantages over the chemical fecal occult blood test. First, it is more sensitive for blood. This means that given the same amount of blood in the stool, the immunologic fecal occult blood test will more frequently be abnormal. In other words, it will more frequently detect cancers and precancerous polyps. Second, it is more specific for blood. That is, there will be fewer abnormal tests due to interfering substances in the diet, and as a result, an abnormal immunologic fecal occult blood test will more commonly be due to cancer or a precancerous polyp. As a result, less follow-up testing (for example, colonoscopy) will be necessary to pursue a falsely abnormal fecal occult blood test.
Source: http://www.rxlist.com
We respect your privacy and aim for the best website experience in compliance with local laws. Allowing cookies enables a tailored experience, while disabling them may reduce personalization. For more information, please read our Privacy Policy and Cookie Policy.