Fecal Occult Blood Test


What Is It?

A fecal occult blood test checks stool samples for traces of blood that cannot be seen with the naked eye. This test is also called a stool guaiac or Hemoccult test. It is a simple chemical test of three consecutive stool samples that involves about five minutes of preparation time for each.

Because the fecal occult blood test can detect bleeding from almost anywhere along the length of the digestive tract, several conditions can cause the result to be positive. They include esophagitis, gastritis, peptic ulcer disease, stomach cancer, ulcerative colitis, colorectal cancer or polyps, and hemorrhoids. The result also can be positive when someone has been taking aspirin or other medications that irritate the digestive tract.

Fecal Occult Blood TestA fecal occult blood testing kit,
used to collect stool samples.

What It’s Used For

The fecal occult blood test usually is used as a screening test to detect colorectal cancer, especially when the cancer is in its early stages and is not causing any symptoms. Doctors usually recommend an annual fecal occult blood test for all adults beginning at age 50. If you have a higher risk of colorectal cancer because of a personal or family history of colorectal cancer or polyps, your doctor may suggest that you start having fecal occult blood tests earlier, or may recommend that you undergo sigmoidoscopy or colonoscopy to screen for cancer.

Your doctor also may recommend this testing if he or she suspects that you are bleeding from somewhere in your digestive tract. For example, a positive fecal occult blood test may help to explain why a person has developed a low level of red blood cells (anemia).


Do not begin your fecal occult blood test when you have active bleeding from hemorrhoids or an anal fissure or when there is blood in your urine. For women, do not begin testing during your menstrual period or during the first three days after the end of your period. Starting seven days before your fecal occult blood test, avoid taking aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen (Advil, Motrin and others) or naproxen (Aleve, Naprosyn and others). Starting 72 hours before the test, make these dietary changes:

  • Avoid taking more than 250 milligrams of vitamin C per day.
  • Avoid eating red meat (beef or lamb), including liver and processed meats or cold cuts.
  • Avoid eating raw fruits and vegetables, especially melons, radishes, turnips and horseradish.

All of these foods and supplements can produce a positive fecal occult blood test even when there is no bleeding from the digestive tract. This is called a false-positive test.

Toilet-bowl cleaners may affect the results of the test, so they should be removed from the toilet that you will be using to collect stool samples for testing.

How It’s Done

Either your doctor or the testing laboratory will give you a kit to use for collecting stool samples for the fecal occult blood test. You should keep this kit in your bathroom at home or carry it with you while you are away from home during the three days that you have to collect stool samples. Write your name and other required information on the front of the collection slides. Since there are several different testing kits available, be sure to read the instructions carefully before you begin.

Flush the toilet twice before your bowel movement. Then, use one of the small wooden sticks from the kit to collect a small sample of stool. Apply this stool sample to the indicated space on the sampling slide. Repeat this procedure daily for two more days or two more bowel movements, as your doctor directs. Use a different card each day. Between samplings, cover the slides and store them away from heat, light and strong chemicals such as bleach or iodine.

When you have collected three stool samples, seal the test envelope and return the kit to your doctor or testing laboratory. Do not send stool samples in the mail, unless you have a special envelope from your physician.


After a few days, call your doctor or laboratory for test results. If your test is positive, your doctor usually will recommend an additional screening procedure such as colonoscopy.


The fecal occult blood test is safe and painless, since it uses samples taken from your normal daily bowel movements.

When To Call A Professional

Call your doctor if there is a change in your bowel habits, including diarrhea or constipation, during the testing period.

Johns Hopkins patient information

Last revised:

Diseases and Conditions Center

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.