URL of this page: https://medlineplus.gov/lab-tests/fecal-occult-blood-test-fobt/
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A fecal occult blood test (FOBT) looks at a sample of your stool (poop) to check for blood. Occult blood means that you can't see it with the naked eye. And fecal means that it is in your stool. Blood in your stool means there is bleeding in the digestive tract. The bleeding may be caused by a variety of conditions, including: Colorectal cancer is one of the most common types of cancer in the United States. A fecal occult blood test can screen for colorectal cancer to help find the disease early when treatment may be most effective. Other names: FOBT, stool occult blood, occult blood test, Hemoccult test, guaiac smear test, gFOBT, immunochemical FOBT, iFOBT; FIT
A fecal occult blood test is commonly used as a screening test to help find colorectal cancer before you have symptoms. The test also has other uses. It may be done when there is concern about bleeding in the digestive tract from other conditions. In certain cases, the test is used to help find the cause of anemia. And it can help tell the difference between irritable bowel syndrome (IBS), which usually doesn't cause bleeding, and inflammatory bowel disease (IBD), which is likely to cause bleeding. But a fecal occult blood test alone cannot diagnose any condition. If your test results show blood in your stool, you will likely need other tests to diagnose the exact cause.
Your health care provider may order a fecal occult blood test if you have symptoms of a condition that could involve bleeding in your digestive tract. Or you may have the test to screen for colorectal cancer when you don't have any symptoms. Expert medical groups strongly recommend that people get regular screening tests for colorectal cancer. Most medical groups recommend that you start screening tests at age 45 or 50 if you have an average risk of developing colorectal cancer. They recommend regular testing until at least age 75. Talk with your provider about your risk for colorectal cancer and when you should get a screening test. A fecal occult blood test is one or several types of colorectal screening tests. Other tests include: There are pros and cons of each type of test. Your provider can help you figure out which test is right for you.
Usually, your provider will give you a kit to collect samples of your stool (poop) at home. The kit will include instructions on how to do the test. There are two main types of fecal occult blood tests:
It's very important to follow the instructions that come with your test kit. The typical process for gathering a stool sample usually includes these general steps:
A fecal immunochemical test (FIT) does not require any preparation, but a guaiac fecal occult blood test (gFOBT) does. Before you have a gFOBT test, your provider may ask you to avoid certain foods and medicines that may affect the results of the test. For seven days before the test, you may need to avoid:
For three days before the test, you may need to avoid:
There is no known risk to having a fecal occult blood test.
If your results from a fecal occult blood test show that you have blood in your stool, it means you likely have bleeding somewhere in your digestive tract. But that doesn't always mean you have cancer. Other conditions that may cause blood in your stool include ulcers, hemorrhoids, polyps, and benign (not cancer) tumors. If you have blood in your stool, your provider will likely recommend more tests to figure out the exact location and cause of your bleeding. The most common follow-up test is a colonoscopy. If you have questions about your test results, talk with your provider. Learn more about laboratory tests, reference ranges, and understanding results.
Regular colorectal cancer screenings, such as fecal occult blood tests, are an important tool in the fight against cancer. Studies show that screening tests can help find cancer early and may reduce deaths from the disease. If you decide to use fecal occult blood testing for your colorectal cancer screening, you will need to do the test every year. You can buy gFOBT and FIT stool collection kits without a prescription. Most of these tests require you to send a sample of your stool to a lab. But some tests can be done completely at home for quick results. If you're considering buying your own test, ask your provider which one is best for you.
Learn how to cite this page The fecal occult blood test (FOBT) is used to find blood in the feces, or stool. An FOBT finds blood in the stool that you cannot see. Blood in the stool may be a sign of colorectal cancer or another medical problem, such as an ulcer or polyps. Polyps are growths that develop on the inner wall of the colon and rectum. FOBTs are one type of screening tool that doctors use to find colorectal cancer. Regular colorectal cancer screenings are recommended for people age 45 and older. If you have a family history of colorectal cancer or if you have other risk factors of developing colorectal cancer, your doctor may recommend that you start regular screening earlier. Learn more about the colorectal cancer risk factors. What are the types of fecal occult blood tests?There are 2 types of FOBTs, both of which you can do at home: Guaiac-based FOBT. During the test, you place a stool sample on a test card coated with a plant-based substance called guaiac. The card changes color if there is blood in the stool. Then, you send the card back to your doctor's office or the lab for interpreting. Usually, this test is provided to you by your doctor's office or a laboratory. Some guaiac-based FOBTs use flushable pads instead of a card. They are available without a prescription at many drugstores. Results are available to the user right away. Fecal immunochemical test (FIT) or immunochemical FOBT. This test uses a specialized protein called an antibody. This specific protein attaches to hemoglobin, the oxygen-carrying part of red blood cells. A sample of the stool is placed in a tube or on a card and sent away to the doctor or laboratory for testing. The immunochemical test has some benefits over the guaiac test. But both tests are used and can provide information about blood in the stool. What should I avoid before a guaiac-based FOBT?Before a guaiac-based FOBT, you cannot eat some foods or take certain medications. Some substances can cause the test to say there is blood in the stool when there is none. This is called a false-positive result. If you will be taking the guaiac test, talk with your health care team about your diet and the medications you are taking. There are different tests available, and each one has different recommendations for what to avoid. Most of the time, your health care provider will tell you to increase your fiber intake. You will also most likely need to avoid:
For some guaiac-based FOBTs, you will need to avoid certain fruits and vegetables. Ask your health care team or refer to the instructions on your FOBT to know what to avoid and for how long. What should I avoid before an FIT?Before an FIT, you do not need to make any dietary changes but you do need to avoid certain medications. NSAIDs and blood-thinning medications may change the results of your test. Your health care team will let you know what medications to avoid before taking the test. When can I take this test?Talk with your health care team about your medical conditions to decide the best timing for your FOBT. For example, the test should not be taken if you have bleeding hemorrhoids, peptic ulcers, or gastritis. You should also not take the test during your menstrual period. These can give a false-positive result. How to collect your stool for this test?Your health care provider will give you instructions for how to best collect the stool samples for your FOBT, whether you are doing a guaiac test or an immunochemical test. There are different brand names for FOBTs, and the instructions can vary for each one. Guaiac-based FOBT. For a guaiac-based FOBT, you will need to collect 3 stool samples. Usually, these samples need to be collected in a clean container. This means that the sample is not mixed with urine or water from the toilet. Your test package will include an applicator. Use the applicator to put a sample of your stools on the provided cards or slides. Package the cards as directed and mail them back to your health care provider or the laboratory. Sometimes, the guaiac FOBT will be done with flushable wipes. After a bowel movement, drop the provided wipe into the toilet. The wipe will change color if blood is present in the stool. Record the results for 3 bowel movements and send the information to your health care provider. FIT. For an FIT, you will need to collect 2 to 3 stool samples. This stool sample can be collected from the toilet using the applicator tool that was included in your kit. You will apply the sample to the container or card provided. Package the samples as directed and mail them to the laboratory. What should I expect after the procedure?You can resume your normal activities right after completing the FOBT. After learning the results, talk with your health care team about whether there are any next steps to take. Questions to ask your health care teamBefore having an FOBT, consider asking the following questions:
Related ResourcesCancer Screening Guide to Colorectal Cancer More InformationU.S. Centers for Disease Control and Prevention: Colorectal Cancer Screening Tests |