Print OverviewThe fecal occult blood test (FOBT) is a lab test used to check stool samples for hidden (occult) blood. Occult blood in the stool may indicate colon cancer or polyps in the colon or rectum — though not all cancers or polyps bleed. Typically, occult blood is passed in such small amounts that it can be detected only through the chemicals used in a fecal occult blood test. If blood is detected through a fecal occult blood test, additional tests may be needed to determine the source of the bleeding. The fecal occult blood test can only detect the presence or absence of blood — it can't determine what's causing the bleeding. A fecal occult blood test isn't recommended if you have colon cancer symptoms. If you notice blood in your stool or in the toilet or if you experience abdominal pain or a change in your bowel habits, make an appointment with your doctor.Products & ServicesA Book: Mayo Clinic on Digestive HealthSign up for Email: Get Your Free Resource – Coping with CancerShow more products from Mayo Clinic Why it's doneThe fecal occult blood test is one option for colon cancer screening. It may be an option if you have an average risk of colon cancer and don't have any symptoms. The fecal occult blood test is typically repeated yearly.More InformationColon polypsCrohn's disease Request an appointment RisksRisks and limitations of the fecal occult blood test include: The test isn't always accurate. Your fecal occult blood test could show a negative test result when cancer is present (false-negative result) if your cancer or polyps don't bleed. Your test could show a positive result when you have no cancer (false-positive result) if you have bleeding from other sources, such as a stomach ulcer, hemorrhoid, or even blood swallowed from your mouth or your nose. Having a fecal occult blood test may lead to additional testing. If your fecal occult blood test result is positive, your doctor may recommend a test to examine the inside of your colon, such as a colonoscopy. How you prepareVarious foods, dietary supplements and medications can affect the results of some fecal occult blood tests — either indicating that blood is present when it isn't (false-positive) or missing the presence of blood that's actually there (false-negative). Your doctor may ask you to avoid certain foods or medicines. To ensure accurate test results, follow your doctor's instructions carefully. 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 you can expect Fecal occult blood test kit Enlarge image Close Fecal occult blood test kit Fecal occult blood test kit This simple fecal occult blood test kit may be used at home. First, you place the sheet of special paper on top of the water in the toilet bowl. After you have a bowel movement, you use the sampling stick to collect a small amount of stool that has been deposited on the floating paper. You then place the sampling stick with the stool sample in the collection container and snap the cap in place. You may either return the sample to your doctor or send it directly to the lab for analysis. There are several types of fecal occult blood tests, each with a different approach to collecting and testing stool. They include: Immunochemical fecal occult blood test (iFOBT, or FIT). The collection method for this test may depend on the manufacturer, but typically, you use a special spoon or other device to collect a sample of stool 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 lab, by mail or in person. Immunochemical testing is preferred over the guaiac fecal occult blood test because it's more sensitive. Also, it doesn't require any dietary restrictions before sample collection and testing can often be performed on a random stool sample. Guaiac fecal occult blood test (gFOBT). For this test, your doctor typically gives you test cards that are used to collect stool samples from multiple bowel movements. You collect a stool sample from each of two or three bowel movements in a clean container, usually taken on consecutive days, and then use an applicator stick to apply a smear of stool to a specific area of a card. After the samples are dry, you return them to your doctor or a designated lab, by mail or in person. Flushable reagent pad or tissue. You can get this kit at a store without a prescription. You place the pad or tissue in the toilet bowl after a bowel movement, usually on three consecutive days. The pads change color when blood is present. You then report the changes to your doctor, usually on a mail-in form. For accurate results, follow the instructions and return the samples promptly. ResultsYour doctor will review the results of the fecal occult blood test and then share the results with you. Negative result. A fecal occult blood test is considered negative if no blood is detected in your stool samples. If you have an average risk of colon cancer, your doctor may recommend repeating the test yearly. Positive result. A fecal occult blood test is considered positive if blood is detected in your stool samples. You may need additional testing — such as a colonoscopy — to locate the source of the bleeding. By Mayo Clinic Staff Request an appointment Doctors & Departments May 04, 2022 Print Show references AskMayoExpert. Colon cancer screening (adult). Mayo Clinic; 2019. Feldman M, et al. Colorectal cancer. In: Sleisenger and Fordtran's Gastrointestinal and Liver Disease: Pathophysiology, Diagnosis, Management. 10th ed. Saunders Elsevier; 2016. https://www.clinicalkey.com. Accessed April 16, 2020. Doubeni C. Tests for screening for colorectal cancer. https://www.uptodate.com/search/contents. Accessed March 17, 2020. Colorectal cancer screening (PDQ) – Health professional version. National Cancer Institute. https://www.cancer.gov/types/colorectal/hp/colorectal-screening-pdq. Accessed March 25, 2020. Fecal occult blood tests. American Society for Clinical Oncology. https://www.cancer.net/navigating-cancer-care/diagnosing-cancer/tests-and-procedures/fecal-occult-blood-tests. Accessed March 24, 2020. Related Colon polyps Crohn's disease Fecal occult blood test kit Products & Services A Book: Mayo Clinic on Digestive Health Sign up for Email: Get Your Free Resource – Coping with Cancer Show more products and services from Mayo Clinic Mayo Clinic in Rochester, Minnesota, has been recognized as the best Gastroenterology & GI Surgery hospital in the nation for 2023-2024 by U.S. News & World Report. Learn more about this top honor Fecal occult blood testAboutDoctors&Departments Advertisement Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission. 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