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U.S. Department of Health and Human Services

Medical Devices

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Fecal Occult Blood

What does this test do? This is a home-use test kit to measure the presence of hidden (occult) blood in your stool (feces).

What is fecal occult blood? Fecal occult blood is blood in your feces that you cannot see in your stool or on your toilet paper after you use the toilet.

What type of test is this?This is a qualitative test -- you find out whether or not you have occult blood in your feces, not how much is present.

Why should you do this test? You should do this test, because blood in your feces may be an early sign of a digestive condition, for example abnormal growths (polyps) or cancer in your colon.

How often should you test for fecal occult blood? The American Cancer Society recommends that you test for fecal occult blood every year after you turn 50. Some doctors suggest that you start testing at age 40, if your family is thought to be at increased risk. Follow your doctor's recommendations about how often you test for fecal occult blood.

How accurate is this test? This test is about as accurate as the test your doctor uses, but you must follow the directions carefully. For accurate results, you must prepare properly for the test and get a good stool sample.

Does a positive test mean you have hidden blood in your stool? A positive result means that the test has detected blood. This does not mean you have tested positive for cancer or any other illness. False positive results may be caused by diet or medications. Further testing and examinations should be performed by the physician to determine the exact cause and source of the occult blood in the stool.

If the test results are negative, can you be sure that you do not have a bowel condition? No. You could still have bowel condition that you should know about. You should use this test again in a year.

How do you do this test? There are several different methods for detecting hidden blood in the stool.

In one method, you collect stool samples and smear them onto paper cards in a holder. You then either send these cards to a laboratory for testing or test them at home. If you test them at home, you add a special solution from your test kit to the paper cards to see if they change color. If the paper cards change color, it means there was blood in the stool.

In another method, you put special paper in the toilet after a bowel movement. If the special paper changes color, it indicates there was blood in the toilet.

You will need to test your feces from three separate bowel movements. These bowel movements should be three in a row, closely spaced in time to minimize the time you need to be on the special diet. This is necessary because if you have polyps, they may not bleed all the time. You improve your chances of catching any bleeding if you sample three different bowel movements.

  • Unless you use the method where you put a test solution into the toilet, it is best to catch your feces before it enters the toilet. You can do this by holding a piece of toilet paper in your hand. After you catch it, cut it apart in two places with the little wooden stick you get in the kit. Take a little bit of the feces from each place where you cut it apart and put these bits on one place in the cardboard in the kit. You use the second and third spots on the cardboard for other bowel movements.

What interferes with this test? To get good results with this test, you have to follow the instructions. You may find it difficult because you need to things you do not ordinarily do.

Because the test is for blood, any source of blood will give a positive test. Blood from another source, like bleeding hemorrhoids or your menstrual period will interfere with the test, so you won't be able to tell what made the test positive.

Pay attention to your diet before the test:

  • Eat a high fiber diet, such as one that has cereals and breads with bran.
  • Cook your fruits and vegetables well.
  • Don't eat raw turnips, radishes, broccoli, or horseradish. These foods can make it look like you have hidden blood when you don't.
  • Don't eat red meat. (You may eat poultry or fish). Red meat in your diet can make it look like you have hidden blood when you don't.

Avoid the following drugs for the 7 days before the test—they can make it look like you have hidden blood when you don't:

  • Aspirin
  • Anti-inflammatory drugs, such as Motrin,

Don't take Vitamin C supplements for the 7 days before the test. Then can prevent the test from detecting your hidden blood.

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