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

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.

Colorectal Cancer

Rectal cancer

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Adenomatous Polyp in Colon

Colon polyp

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Possible Complications

There are no major complications associated with this test.

What to Expect

Prior to Test

A positive FOBT does not mean you have cancer. Other things can cause a positive test. Minor stomach bleeding from certain medications, hemorrhoids, or eating certain foods can cause a positive test. To help avoid this, you can try to:

  • Avoid certain medications and foods, such as:     
  • Nonsteroidal anti-inflammatory drugs for 7 days prior to testing. If you are taking them daily for medical conditions, talk to your doctor before you stop taking them.
  • Red meats, cantaloupe, uncooked vegetables, blood sausage, and possibly hot sauce for 3 days before testing
  • Wait until your hemorrhoids are not bleeding.
  • Avoid having the test during your menstrual period.
  • Avoid cleaning your toilet bowl for several days before the test. Chemicals from the cleanser can affect the test.
  • 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 3 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 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

    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?

    The test should only take a few minutes.

    Will It Hurt?

    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

    After the test, call your doctor if any of the following occur:

  • Development of any new symptoms
  • Worsening of existing symptoms
  • In case of an emergency, call for emergency medical services right away.