Fecal Occult Blood Test (FOBT)

You can have blood in your stool and not be able to see it. A fecal occult blood test is an at-home screening used to find the tiniest traces of blood in stool, which is a sign that something is wrong in your digestive tract. FOBT is often used for colorectal cancer screening, but a positive FOBT result on its own isn’t a cancer diagnosis.


What is a fecal occult blood test (FOBT)?

A fecal occult blood test is a screening that looks for hidden (occult) blood in stool (poop). The test can identify tiny traces of blood that you can’t see on your own. It helps healthcare providers diagnose several health conditions.


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What does a fecal occult blood test show?

Blood in the stool means there’s bleeding happening somewhere in your digestive tract. This type of bleeding isn’t normal and is usually a sign of a health condition, such as:

  • Anemia, when your body doesn’t have enough healthy red blood cells.
  • Colitis, inflammation or irritation in your colon.
  • Colorectal cancer, cancer that occurs in the lower part of your colon or rectum.
  • Diverticulosis, an expanded, bubble-like area on your colon wall.
  • Hemorrhoids, swollen veins inside your rectum or outside your anus.
  • Colon polyps, a flat, raised or stalk-like growth on your colon or rectal lining.
  • Ulcers, sores that develop in the digestive tract or rectum.

What is the purpose of a fecal occult blood test?

If you have certain symptoms, such as abdominal pain, fatigue, pain around your rectum or rectal bleeding, your healthcare provider may recommend a fecal occult blood test. The most common reason for an FOBT is to screen for colorectal cancer.

On its own, a fecal occult blood test can’t diagnose colorectal cancer or any digestive issue. Depending on the results of your FOBT, you may need more testing to confirm a diagnosis.


Should I get a fecal occult blood test regularly?

For people between 45 and 75 who are at average risk of colorectal cancer, the U.S. Preventive Services Task Force recommends regular screening. You’ll do the test once a year. If you’re older than 75 or have a higher risk of developing colorectal cancer, talk to your provider about the screening schedule that’s right for you.

If you’re unsure what your risk level is, your healthcare provider can help you figure out how often you should get screened.

Who performs a fecal occult blood procedure?

You can perform the FOBT at home. You then send the completed test kit to your provider or laboratory by dropping it off or mailing it.

You can also collect your stool sample at home without testing it. You then send the sample to a laboratory to complete the screening.


Test Details

What are the types of fecal occult blood tests?

There are three types of FOBTs:

  • Guaiac fecal occult blood test (gFOBT): Detects hidden blood in the stool using a chemical called guaiac.
  • Fecal immunochemical test (iFOBT or FIT): Finds traces of blood in the stool using antibodies.
  • FIT-DNA: Screens for DNA alterations associated with colorectal cancer.

Where can I get a fecal occult blood test kit?

You can buy gFOBT and iFOBT kits over the counter (without a prescription). Check your local pharmacies. You can get the tests yourself, but you still need to send the completed sample to your provider or laboratory.

How do I prepare for a fecal occult blood test?

If you are doing an iFOBT/FIT test, you don’t need to adjust your diet.

You might need to adjust your diet and medications before having a gFOBT — some food and medications can cause a false positive. Talk to your healthcare provider before stopping any medication. Ask your provider if there are other foods or medications you should avoid and for how long.

In the days leading up to the gFOBT test, increase your fiber and decrease:

  • Blood-thinning medications (after talking to your provider).
  • Nonsteroidal anti-inflammatory drugs (NSAIDs) including aspirin, ibuprofen and naproxen.
  • Red meat.
  • Vitamin supplements like iron and vitamin C.

How does a fecal occult blood test work?

To do a gFOBT test at home:

  1. Carefully read the instructions that came with the testing kit. They may vary slightly from these instructions.
  2. Collect your stool in a dry, clean container. Some kits come with special paper to place in your toilet to catch the bowel movement. You can’t use stool mixed with urine or toilet water.
  3. Use the applicator stick in the test kit to wipe a small amount of stool on the inside of the testing card.
  4. Use another applicator stick on a second stool sample. Wipe it on the inside of the second testing card.
  5. Keep the testing cards at room temperature, away from heat and moisture.
  6. Deliver the completed test kit to your healthcare provider or laboratory. Check with your provider for more specific instructions.

The iFOBT/FIT instructions are the same as for gFOBT, but you can use the applicator sticks to take samples directly from the toilet. You need to get at least two to three stool samples. Package and mail the completed test kit to the laboratory as directed.

When should I avoid doing a fecal occult blood test?

Don’t take an FOBT during your period — this can cause a false positive. Also, avoid taking this test if you have:

What should I expect after a fecal occult blood test?

You can go back to your routine after completing the FOBT. You’ll probably have to wait at least a week for the results.

What are the risks of a fecal occult blood test? Are there side effects?

There are no known risks or side effects associated with the FOBT.

Results and Follow-Up

When should I know the fecal occult blood test results?

You can expect to wait at least a week for the results of the FOBT. In some cases, it may take longer. Ask your provider or laboratory how long you can expect to wait for the results.

What does a positive fecal occult blood test mean?

If your FOBT is positive, there could be bleeding in your digestive tract. It may signal colorectal cancer, but it isn’t a cancer diagnosis. Typically, if the result is positive, your provider will call you to talk about next steps.

Usually, the next step after getting a positive result is more testing to find the location and cause of the bleeding. Your provider will discuss this with you.

When should I call my healthcare provider?

If you don’t hear from your provider or laboratory within two weeks of submitting your sample, call them.

Also, if you’re at risk for colorectal cancer and unsure how often to get screened, talk to your healthcare provider.

A note from Cleveland Clinic

If there are tiny traces of blood in your stool (poop), you can’t feel or see them on your own. That’s when a fecal occult blood test can help. Don’t worry, this screening doesn’t hurt. Healthcare providers often use it to help detect signs of colorectal cancer, but it can detect other issues, too. Remember that a positive FOBT result isn’t a cancer diagnosis. Finding hidden blood in your stool means there’s bleeding in your digestive system. With this knowledge, your healthcare provider can use other tests to investigate the bleeding and make a diagnosis.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 09/30/2022.

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