The faecal occult blood test (FOBT) is a laboratory test used to check stool samples for occult (occult) blood. Hidden blood in the stool can indicate colon cancer or polyps in the colon or rectum, although not all cancers or polyps bleed. Occult blood is usually passed in such small amounts that it can only be detected through the chemicals used in a faecal occult blood test.
If blood is detected through a faecal occult blood test, additional tests may be needed to determine the source of the bleeding. The faecal occult blood test can only detect the presence or absence of blood; cannot determine what is causing the bleeding.
A faecal occult blood test is not recommended if you have symptoms of colon cancer. If you notice blood in your stool or toilet bowl, or if you experience abdominal pain or a change in your bowel habits, make an appointment with your doctor.
Why it’s done
The faecal occult blood test is an option for the detection of colon cancer. It may be an option if you are at average risk for colon cancer and don’t have any symptoms. The faecal occult blood test is usually repeated annually.
The risks and limitations of the faecal occult blood test include:
- The test is not always accurate. Your faecal occult blood test may show a negative result when cancer is present (false negative result) if your cancer or polyps do not bleed. Your test could show a positive result when you don’t have cancer (false positive result) or if you have bleeding from other sources, such as a stomach ulcer, haemorrhoids, or even blood swallowed through your mouth or nose.
- Having a faecal occult blood test may lead to additional testing. If your faecal occult blood test result is positive, your doctor may recommend a test to look inside your colon, such as a colonoscopy.
How do you prepare
Various foods, dietary supplements, and medications can affect the results of some faecal occult blood tests, either by indicating that blood is present when it is not (false positive) or by missing the presence of blood that is actually there (false negative). ). Your doctor may ask you to avoid certain foods or medicines. To ensure accurate test results, carefully follow your doctor’s instructions.
For about three days before the test, your doctor may ask you to avoid:
- Certain fruits and vegetables, including broccoli and turnips
- Red meat
- Vitamin C Supplements
- Pain relievers, such as aspirin and ibuprofen (Advil, Motrin IB, others)
What can you expect
There are several types of faecal occult blood tests, each with a different approach to collecting and analyzing stool. They include:
- Immunochemical faecal occult blood test (iFOBT or FIT). The collection method for this test can depend on the manufacturer, but typically, you use a special spoon or another device to collect a stool sample and store it in a collection container that comes with the test kit. The collection container is then returned to your doctor or a designated laboratory, by mail or in person. Immunochemical tests are preferred over the guaiac faecal occult blood test because it is more sensitive. Additionally, it does not require any dietary restrictions before sample collection and testing can often be performed on a random stool sample.
- Guaiac faecal occult blood test (gFOBT). For this test, your doctor usually gives you test cards that are used to collect stool samples from multiple bowel movements. Collect a stool sample from each of two or three bowel movements into a clean container, usually on consecutive days, and then use an applicator to apply a stool sample to a specific area on a card. After the samples are dry, you return them to your doctor or to a designated laboratory, by mail or in person.
- Disposable reagent pad or tissue. You can get this kit at a store without a prescription. Place the pad or tissue in the toilet bowl after a bowel movement, typically for three consecutive days. The pads change colour when there is blood. You then report the changes to your doctor, usually on a form in the mail. For accurate results, follow instructions and return samples promptly.
Your doctor will review the results of the faecal occult blood test and then share the results with you.
- Negative result. A faecal occult blood test is considered negative if no blood is detected in the stool samples. If you are at average risk for colon cancer, your doctor may recommend repeat testing annually.
- Positive result. A faecal occult blood test is considered positive if blood is detected in stool samples. You may need additional tests, such as a colonoscopy, to locate the source of the bleeding.