Also called stool guaiac test or a guaiac smear.
Fecal occult blood testing (FOBT) is testing that is performed on samples of stool in order to detect occult blood (traces of blood that are not visible without a microscope) 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, and hence 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).
If the test is performed in an office or hospital, stool may be collected by a doctor during an examination.
If the test is performed at home, a stool sample from three consecutive bowel movements is collected, smeared on a card, and mailed to a laboratory for processing. 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 many ways to collect the samples. You can catch the stool on plastic wrap that is loosely placed over the toilet bowl and held in place by the toilet seat. Then put the sample in a clean container. One test kit supplies a special toilet tissue that you use to collect the sample, then put the sample in a clean container. Do not take stool samples from the toilet bowl water, because this can cause errors.
For infants and young children wearing diapers, you can line the diaper with plastic wrap. The plastic wrap is positioned so that it keeps the stool away from any urine. Mixing of urine and stool can spoil the sample.
Laboratory procedures may vary. There are two types of fecal occult blood testing, 1) chemical and 2) immunologic.
1. Chemical testing: For chemical testing, a solution containing the chemical guaiac and an oxidizing chemical is used. If blood is present in the sample of stool, the mixing of the solution with blood causes the guaiac to turn visibly blue. The blue color is caused by the interaction (promoted by the oxidizing agent) of the heme portion of the hemoglobin molecule, the oxygen carrying molecule in red blood cells, and the guaiac.
2. Immunologic testing: For immunologic testing, a sample of stool is mixed with a solution that contains an antibody to globin, the protein part of the hemoglobin molecule. The antibody is combined with a small amount of gold. When the antibody/gold complex binds to the globin in stool, the antibody/gold/globin complex settles out of the solution as a visible line on the test strip.
Do not eat red meat, any blood-containing food, cantaloupe, uncooked broccoli, turnip, radish, or horseradish for 3 days prior to the test. You may need to stop taking medicines that can interfere with the test. These include vitamin C and aspirin. Check with your health care provider regarding medication changes that may be necessary. Never stop or decrease any medication without consulting your health care provider.
There is no discomfort when the test is done at home, because this test only involves normal bowel functions. If stool is collected during an exam, there may be some discomfort in the anal canal and rectum.
A negative test result means that there is no blood in the stool. Abnormal results may indicate angiodysplasia of the GI tract, esophageal varices, esophagitis, gastritis, GI infections, GI trauma, peptic ulcers and other conditions. Fecal occult testing is sometimes used to screen for colon cancer, but it is not a reliable test for this purpose, and other screening methods should be used. Abnormal tests require follow-up with your doctor.
The only downside of fecal occult blood tests is when tests show a false positive (showing blood). Every test showing blood requires a colonoscopy, an expensive procedure that carries a small but definite risk of serious complications. A 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). It is important to remember that having occult blood in the stool does not automatically imply that one has colon cancer or a polyp.
Acid Reflux Test - Fecal Occult Blood Test References
By Mortin - Copyright 2009
Last modification 31/12/2009