Everything You Need to Know About a Fecal Occult Blood Test (FOBT)

Sometimes cancers or polyps bleed. An FOBT checks for blood in your stool. It’s a highly sensitive test, which means it can find polyps and cancer. However, sometimes the test can indicate that there’s a polyp or cancer when there isn’t. This is called a false positive. Or it can miss a polyp that doesn’t bleed. Therefore it’s commonly used as an initial test before another screening test such as a colonoscopy or a sigmoidoscopy.

Another type of FOBT, also called a fecal immunochemical test, checks for a certain protein in your stool rather than in your blood. This test has fewer false positives, but it still misses polyps that don’t bleed.

How to Do the Test

You can do an FOBT at home using an FOBT test from a pharmacy. It’s easy to perform, but it can be somewhat unpleasant because it involves collecting samples of your own stool. Each test has slightly different instructions, and it’s very important to follow the instructions exactly to get accurate results. Generally, FOBTs work in the following way.

• You’ll start by collecting 3 stool samples--2 if you’re doing a fecal immunochemical test. You can do this by using a clean container or by draping plastic wrap loosely across your toilet bowl to catch your stool. The process may take several days depending on how often you have a bowel movement.

• Using the test applicators, you’ll take 2 samples from different parts of each of the stools you collected. Then you’ll smear the samples on the testing cards in your kit.

• Some testing cards come with a chemical solution. When you apply it to the cards that hold the samples, the cards turn blue if there is blood in your stool. If there is no chemical solution, you will have to return the sealed cards to your doctor by mail or in person to get your results.

• If you’re able to get the results at home and the cards do turn blue, you should contact your doctor right away.

What to Do to Get the Most Accurate Results

To make sure you get the most accurate results, follow these guidelines when you prepare for the test.

• Don’t eat turnips, beets, radishes, and horseradish for 2 to 3 days before the test.

• Don’t eat red meat for 2 to 3 days before the test. Small amounts of chicken, turkey, or fish are OK.

• Don’t take iron or vitamin C supplements for 3 days before the test.

• Don’t use products that contain aspirin or use nonsteroidal anti-inflammatories, also called NSAIDs, such as ibuprofen, for 7 days before the test.

• Don’t do the test if you are having your period or have active hemorrhoids.

• Don’t test a stool sample that comes in contact with toilet-bowl-cleaning products that turn water blue.