A fecal occult blood test (FOBT) looks for blood in the stool.

Reasons for Test

The test is used to screen for colon and rectal cancers.

It may also be used to help find cause for belly pain, diarrhea, vomiting, or lack of hunger.

Colon Cancer in the Rectal Wall
Rectal cancer

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Polyp in the Colon Wall
Colon polyp

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Possible Complications

There are no major problems linked to having this test.

What to Expect

Prior to Test

Certain food and medicine can affect the test. You may be asked to AVOID:

  • Nonsteroidal anti-inflammatory drugs (NSAIDs) for 7 days before testing. If you take then for health problems, talk to your doctor before you stop taking them.
  • Red meats, cantaloupe, uncooked vegetables, blood sausage, and hot sauce. You may need to avoid for 3 days before testing

Other steps to help get accurate results include:

  • Wait until your hemorrhoids are not bleeding.
  • Avoid having the test during your menstrual cycle.
  • Avoid cleaning your toilet bowl for a few days before the test. They can affect the test.

Description of Test

The test is most often done at home. Follow instructions that are provided with your kit. The following is a general explanation.

When you are ready to have a bowel movement, you will set up the kit using the instructions. The kit should allow you to collect 3 samples. Some kits have a disposable container into which you can pass your bowel movement. Other kits give you tissue paper or plastic wrap that you can lay in the toilet to keep your stool from getting into the water.

You can also turn off the water valve to the toilet tank and flush the toilet a couple of times. This will empty most of the water out of the toilet bowl. When ready, pass the stool into the bowl. Collect the sample, then turn the water back on.

Using thin wooden sticks from the kit, you will pick up a small sample of stool. You will then smear the sample onto a special card. The card folds over to protect the stool sample.

After Test

The card may need to be mailed or brought into a clinic. 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 need more tests. These tests will help to find out the cause of the bleeding. Although cancer may be one cause of blood in the stool, there are many other less serious causes.

Call Your Doctor

Call your doctor if you have:

  • Any new symptoms
  • Worsening of current symptoms

If you think you have an emergency, call for emergency medical services right away.


Family Doctor—American Academy of Family Physicians

National Institute on Aging


Canadian Digestive Health Foundation

Health Canada


Colorectal cancer screening. EBSCO DynaMed Plus website. Available at: Updated May 21, 2018. Accessed July 20, 2018.

Colorectal cancer screening tests. American Cancer Society website. Available at: Updated May 30, 2018. Accessed July 20, 2018.

Fecal occult blood test and fecal immunochemical test. Lab Tests Online—American Association for Clinical Chemistry website. Available at: Updated July 13, 2018. Accessed July 20, 2018.

Last reviewed May 2018 by EBSCO Medical Review Board James Cornell, MD  Last Updated: 7/20/18