Fecal Occult Blood Test
(FOBT; Stool Occult Blood Test)
by Amy Scholten, MPH
A fecal occult blood test (FOBT) is a test to detect the presence of blood in the stool, also known as the feces.
Reasons for Test TOP
An FOBT is used as part of the colorectal cancer screening process.
It may also used to detect blood in your stool if you are having abdominal pain, diarrhea, vomiting, decreased appetite, or other symptoms.
Possible Complications TOP
There are no major complications associated with this test.
What to Expect TOP
Prior to Test
A positive FOBT does not mean you have cancer. Other things can cause a positive test. Minor stomach bleeding from certain medicines or hemorrhoids or eating certain foods can cause a positive test. To help avoid this, you can try to:
Description of Test
The test is most often done at home.
When you are ready to have a bowel movement, you will set up the kit according to the instructions. The kit should allow you to collect three samples of stool. Some kits provide a disposable container into which you can pass your bowel movement. Other kits provide you with tissue paper or plastic wrap that you can lay in the toilet to keep your stool sample from sinking into the water.
Using thin wooden sticks provided with the kit, you will pick up a very small sample of stool. You will then smear the sample onto a special card. If you do not have hemorrhoids some doctors may allow you to smear the sample onto the card with stool from toilet paper. The card folds over to protect the stool sample.
After Test TOP
You will mail or deliver the cards to the clinic or lab. Make sure you have written your name on each card.
How Long Will It Take? TOP
The test should only take a few minutes.
Will It Hurt? TOP
This test will not hurt.
If blood is found in your stool, you may be asked to have additional tests. These tests will help to determine the cause of the bleeding. Although cancer may be one cause of blood in the stool, there are many other causes.
Call Your Doctor TOP
After the test, call your doctor if any of the following occur:
In case of an emergency, call for medical help right away.
American Academy of Family Physicians
National Institutes of Health
Canadian Digestive Health Foundation
Can colorectal polyps and cancer be found early? Colorectal cancer screening. American Cancer Society website. Available at:
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Updated January 17, 2013. Accessed April 26, 2013.
Guide to diagnostic tests: fecal occult blood test. Harvard Medical School Health Publications website. Available at: https://www.health.harvard.edu/diagnostic-tests/fecal-occult-blood-test.htm. Accessed on April 26, 2013.
Pignone M, Campbell M, Carr C, et al. Proposed Effects of Dietary and Medication Restrictions during FOBT with guaiac-based tests. Meta-analysis of dietary restriction during fecal occult blood testing. Effective Clinical Practice . 2001;4:150-156.
Last reviewed February 2014 by Michael Woods, MD
Last Updated: 3/18/2013