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The fecal occult blood test is a commonly used test to detect small amounts of blood in the stool, which are not visible to the naked eye, for the purpose of screening colorectal cancer.
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The Hemoccult test is an examination aimed at detecting very small amounts (traces) of blood in the stool, which are invisible to the naked eye. It is an extremely useful test for screening for colon and rectal cancer before symptoms appear.
Adenomas (benign) and colon cancer (malignant) can cause light bleeding that can be detected in the stool. These quantities are generally too small to be visible to the naked eye, which is why we speak of “occult blood”.
The two main types of tests available on the market for fecal occult blood test (FOBT) are Gaiac tests and qualitative or quantitative immunological tests.
It is important to note that the stool test for occult blood is only a screening test. If the result is positive, the doctor usually suggests further tests, such as a colonoscopy, to confirm the diagnosis.
1- This test is carried out with the aim of detecting colorectal cancers in asymptomatic people, and it is generally recommended to repeat it every year.
As recommended by the CDC , this test is recommended for anyone with:
2- This test can also be prescribed when a person has anemia to assess the possibility of digestive bleeding.
Note: If symptoms are present (visible blood in the stool or abdominal pain), other more appropriate tests, such as a colonoscopy, are generally recommended.
To avoid potential interactions and false results during the fecal occult blood test, here are some steps your doctor may recommend:
There are 3 main types of FOBT tests:
This is the most common type of test for fecal occult blood. Guaiac tests are based on the enzymatic activity of a compound present in red blood cells: heme (a cofactor linked to globin).
The test includes a paper impregnated with Guaiac resin. In the presence of blood in the stool, heme reacts with the added hydrogen peroxide, and its pseudo-peroxidase activity leads to the formation of a colored compound on the strip.
To obtain a reliable result, it is generally necessary to take two separate stool samples from three successive stools. A blue color appears in less than one minute if occult blood is present.
Modern, highly sensitive versions of the Gaiac test have much higher detection rates for colorectal cancer and adenomas than older versions.
| Guiac-based FOBT | Cancer Susceptibility | Adenoma Susceptibility |
|---|---|---|
| High sensitivity hemoccult | 50% - 79% | 21% - 35% |
| Hemoccult II | 13% - 50% | 8 % - 20% |
The immunochemical fecal occult blood test (iFOBT) uses antibodies against human hemoglobin to detect blood in the stool
This test does not require any restrictions in diet, medication, or vitamins.
| iFOBT and guaiac test | Cancer Susceptibility | Adenoma Susceptibility |
|---|---|---|
| iFOBT | 55% - 100% | 15% - 44% |
| High sensitivity guaiac test | 50% - 79% | 21% - 35% |
This method is based on the combination of a test to detect genetic material (DNA) associated with colorectal cancer with an immunochemical test for occult blood in the stool. The person collects the samples for this test at home using a kit, then sends the samples to the laboratory.
The presence of occult blood in the stools actually means that there is bleeding somewhere in the digestive tract. This bleeding can be caused by a variety of conditions, including:
When occult blood is detected in the stool, additional testing is usually necessary to diagnose the specific cause of the bleeding. These tests may include:
In conclusion, fecal occult blood testing is an essential test for early detection of colorectal cancer and other gastrointestinal conditions.
When occult blood is detected, additional tests, such as endoscopies, blood tests and examinations medical imaging, are often necessary to diagnose the precise cause of bleeding and develop an appropriate treatment plan
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