What Can Give a False Reading for Fecal Occult Blood Test
- What Is It?
- What is a fecal occult claret test?
- Uses
- Why is fecal occult claret testing done?
- How should fecal occult blood tests be used?
- Procedure
- How is a fecal occult claret exam performed?
- Chemic Fecal Occult Claret Test
- How do the results of chemical fecal occult blood testing compare with immunologic fecal occult blood testing?
- Effectives and Benefits
- How effective are fecal occult claret tests?
- Heart
- Fecal Occult Blood Test Center
- Comments
- Patient Comments: Fecal Occult Blood Test - Indications
What is a fecal occult blood test?
The underlying cause of the change in stool color, texture, or class is responsible for whatever symptoms. Source: Getty Images
Fecal occult blood testing (FOBT) is testing that is performed on samples of stool in order to detect occult claret (blood that is not visible to the naked eye) in the otherwise normal-colored stool. Fecal occult blood usually is a consequence of dull (often intermittent) bleeding from inside the upper or lower gastrointestinal tract. The ho-hum bleed does not change the color of the stool or outcome in visible bright red blood. Therefore, the blood is found just by testing the stool for blood in the laboratory. Occult haemorrhage has many of the same causes equally other forms of more rapid gastrointestinal haemorrhage, such equally rectal bleeding (passage of crimson blood and/or blood clots rectally) and melena (black tarry stool as a event of bleeding from the upper intestines such equally ulcers). Delight read the Rectal Bleeding commodity for a more detailed explanation of different patterns of gastrointestinal bleeding.
Why is fecal occult blood testing washed?
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A fecal occult blood test is done primarily to detect colon cancer in people without intestinal symptoms. Cancers of the colon are mutual and frequently produce fecal occult blood long earlier they crusade other symptoms such as
- abdominal pain,
- rectal haemorrhage, or
- changes in bowel habits.
In addition, some precursors of colon cancer, specifically, some types of colon polyps, as well may drain slowly and crusade fecal occult claret.
- By finding the cancers early on 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 constitute through fecal occult claret testing, cancer may be prevented.
How is a fecal occult blood examination performed?
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For fecal occult claret testing, several (usually 3) samples of stool are collected for testing. The reason for testing multiple samples is that bleeding from cancers and polyps frequently is intermittent and only one of the samples may show blood.
There are two types of fecal occult blood testing including:
- Chemical testing: For chemical testing, a solution containing the chemical guaiac and an oxidizing chemical is used. If claret is present in the sample of stool, the mixing of the solution with blood causes the guaiac to turn visibly blueish. The bluish color is caused by the interaction (promoted by the oxidizing amanuensis) of the heme portion of the hemoglobin molecule, the oxygen-carrying molecule in red blood cells, and the guaiac.
- 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 antibiotic is combined with a small amount of gold. When the antibiotic/gilded complex binds to the globin in stool, the antibody/gold/globin complex settles out of the solution equally a visible line on the exam strip.
How do the results of chemical fecal occult blood testing compare with immunologic fecal occult claret testing?
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A chemic fecal occult blood test is inexpensive and easy, just it has several disadvantages.
- Substances in fruits and vegetables can mimic heme and cause chemical fecal occult blood tests to be falsely positive, that is, falsely aberrant. Therefore, information technology is necessary to restrict certain fruits and vegetables before and during the collection of stool samples.
- Unlike heme which can travel intact from the stomach or small intestine and into the stool, globin is destroyed in the small intestine. As a result, a positive chemical fecal occult blood test can be caused past bleeding anywhere in the stomach or intestines, only a positive immunologic fecal occult blood test simply occurs when there is bleeding into the colon. Therefore, information technology is necessary to restrict red meat containing hemoglobin earlier and during the collection of stool samples, or the heme from the ingested meat will cause a falsely positive examination.
- Some drugs commonly crusade modest amounts of bleeding into the stomach or small intestine. Moreover, vitamin C and a few other drugs can cause aberrant chemic fecal occult blood tests. Therefore, these drugs must be stopped before and during the collection of samples.
The immunologic fecal occult blood test has additional advantages over the chemical fecal occult blood test.
- First, it is more than sensitive to blood. This means that given the same corporeality of claret in the stool, the immunologic fecal occult blood test will more than ofttimes be abnormal. In other words, information technology will more oftentimes notice cancers and precancerous polyps.
- Second, it is more specific for blood. That is, in that location will be fewer abnormal tests due to interfering substances in the diet, and as a outcome, an abnormal immunologic fecal occult blood test will more than commonly be due to cancer or a precancerous polyp.
As a result, less follow-up testing (for instance, colonoscopy) will be necessary to pursue a falsely abnormal fecal occult blood test.
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How constructive are fecal occult blood tests?
The true bottom line for a fecal occult blood exam is how many cancers or precancerous polyps can be detected and, ultimately, how many cancer-related deaths tin exist prevented by fecal occult blood tests.
- Large studies with chemic fecal occult claret tests have demonstrated at least a 15%-xx% reduction in mortality due to colon cancer.
- Similar studies are now underway with immunologic fecal occult blood tests, and, based on factors discussed previously, the results are expected to exist meliorate.
- However, the results of these ongoing studies are necessary to demonstrate what the bottom line truly is for immunologic fecal occult claret tests.
How should fecal occult blood tests exist used?
Fecal occult blood tests offer an important screening modality for colon cancer, only, because it detects only a minority of cancers and precancerous polyps, past itself information technology is not sufficient. Information technology needs to be complemented past endoscopic exam of the colon, either sigmoidoscopy and/or colonoscopy.
Recommendations for the age at which fecal occult blood tests and endoscopic examinations should be initiated, and the frequency with which they should exist repeated depending on the risk for colon cancer. Patients who are older, have relatives with colon cancer, have had polyps previously, or have diseases that are associated with a higher risk for colon cancer may have testing that begins earlier and is done more frequently.
The apply of fecal occult blood tests has only one downside. Tests tin can be falsely positive, that is, tests that show claret in patients who don't take colon cancer or premalignant polyps. Every test showing blood requires the performance of colonoscopy, an expensive procedure that carries a minor only definite gamble of serious complications. The more oft tests are falsely positive, the more than often unnecessary colonoscopies are performed. If studies underway (discussed previously) demonstrate an increased ability to diagnose cancer and colon polyps with a reduced frequency of these falsely positive tests, at that place will exist clear advantages for immunologic over chemical fecal occult blood tests. For this reason, immunologic fecal occult blood tests accept advantages over chemical fecal occult blood tests since information technology has fewer false-positive tests.
Information technology is important to remember that having occult blood in the stool does non automatically imply that one has colon cancer or a polyp. There are many causes of occult claret in the stomach, small intestine, or colon, most of which are benign. Some examples include
- bleeding from the use of aspirin or other nonsteroidal anti-inflammatory drugs (for instance, ibuprofen),
- ulcers,
- esophagitis,
- colitis, and
- intestinal angiodysplasias (weakened clusters of blood vessels on the surface of abdominal linings).
Therefore, patients with stools containing occult blood should exist evaluated by physicians to exclude cancers and polyps, too every bit to identify other causes of intestinal bleeding.
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Medically Reviewed on 12/half-dozen/2021
References
Medically reviewed past Avrom Simon, Dr.; Board Certified Preventative Medicine with Subspecialty in Occupational Medicine
REFERENCE:
"Tests for screening for colorectal cancer: Stool tests, radiologic imaging and endoscopy"
UptoDate. Updated Aug 23, 2016.
Source: https://www.medicinenet.com/fecal_occult_blood_tests/article.htm
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