Fecal Occult Blood Test (FOBT): About This Test

What is it?

A guaiac fecal occult blood test checks for hidden (occult) blood in the stool. You place a small sample of stool on a chemically treated card, pad, or wipe. Then a chemical solution is put on top of the sample. If the card, pad, or wipe changes color, there is blood in the sample.

Why is this test done?

A guaiac fecal occult blood test is done to look for signs of colorectal cancer and other types of gastrointestinal problems. These include hemorrhoids, anal fissures, and colon polyps, which can cause blood in the stools.

The test isn't able to diagnose colorectal cancer. If a gFOBT finds blood in the stool, you may need more tests to find the reason for the bleeding.

How do you prepare for the test?

Before you do a guaiac fecal occult blood test, you may need to avoid the following things for 2 to 3 days before the test:

• Eating turnips, beets, radishes, horseradish, artichokes, mushrooms, broccoli, bean sprouts, cauliflower, apples, oranges, bananas, grapes, and melon. These foods can cause the test to be positive for blood when blood is not in the stool.
• Eating red meat. This may cause false test results. Small amounts of chicken, turkey, or fish will not affect the test.
• Taking iron supplements
• Taking aspirin (or products that contain aspirin) and nonsteroidal anti-inflammatory drugs (NSAIDs). Also avoid taking other medicines that irritate the stomach or intestines.
• Taking vitamin C supplements

Don't do the test during your menstrual period or if you are having bleeding from hemorrhoids. And don't test a stool sample that has been in contact with toilet bowl cleaning products that turn the water blue.

How is the test done?

You can check for blood in your stool at home. There are different types of home tests you can use. Make sure to follow the instructions that come with any test. For most tests, you will use stool samples from three different bowel movements over three different days.

For any home test, follow these guidelines:

• Check the expiration date on the package. Don't use a test kit after its expiration date.
• Store the test kit as instructed. Many kits have to be stored in a refrigerator or cool place.
• Follow the instructions exactly. Do all the steps in order, without skipping any of them. Be aware of any special things you need to do before the test. This may include not eating certain foods or limiting your physical activity.
• After you finish your test, follow the instructions that you were given for returning the test.

For a gFOBT test, you put a small sample of stool a card that comes with the kit. You return this to your doctor or a lab.

Other test kits

• Some kits tell you to use a special cloth to wipe with after a bowel movement. After you wipe with the cloth, you put the developer solution on it to check for a color change that means there is blood in the stool.
• Other kits have a special test pad that you place in the toilet after a bowel movement. The pad will change color if the stool has blood in it.