Fecal Occult Blood Test (FOBT)
Reviewed
Also called: FOBT, stool occult blood test, Hemoccult test, guaiac smear test, gFOBT, immunochemical FOBT (iFOBT or FIT)
A fecal occult blood test (FOBT) checks for blood in a sample of your stool (poop). Blood in your stool means there is bleeding in the digestive tract.
Specimen: Stool (feces)
Why this test may be ordered
- Screening for colorectal cancer (starting at age 45 for average risk, or earlier for higher risk).
- To investigate symptoms of digestive tract bleeding (e.g., anemia, change in bowel habits).
- To help distinguish irritable bowel syndrome from inflammatory bowel disease.
Preparation and collection
You do not need any special preparations for many fecal occult blood tests. But for some guaiac fecal occult blood tests (gFOBTs), certain foods, supplements, and medicines may affect the results of the test. If you are having one of these tests, your provider will tell you what you need to avoid and for how long. If you take aspirin for heart problems, talk with your provider before stopping your medicine.
Usually, your provider will give you a kit to collect samples of your stool (poop) at home. Different test kits have different instructions, so it's very important to follow the specific instructions that come with your kit.
There is no known risk to having a fecal occult blood test.
Understanding results
A fecal occult blood test can screen for colorectal cancer to help find the disease early, when treatment may be most effective.
- Blood found in stool (positive): 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. Limitation: 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. Next step: 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.
- No blood found (routine screening): If you decide to use fecal occult blood testing for your colorectal cancer screening, you will need to do the test every year. Limitation: Studies show that screening tests can help find cancer early and may reduce deaths from the disease. Next step: If you're considering buying your own test, ask your provider which one is best for you.
- FOBT is a screening test only; it cannot diagnose any condition. A positive result requires follow-up testing (e.g., colonoscopy) to find the cause of bleeding.
- False-positive results can occur due to certain foods, supplements, or medicines (especially with guaiac-based tests).
- False-negative results can occur if bleeding is intermittent or if the sample is not collected correctly.
What to do next
If you have questions about your test results, talk with your provider.
- What does my result mean for my risk of colorectal cancer?
- Do I need any follow-up tests based on my result?
- How often should I repeat this screening test?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.
U.S. National Library of Medicine: Fecal Occult Blood Test (FOBT)