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.
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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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:
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.
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.
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.
There are three types of FOBTs:
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.
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:
To do a gFOBT test at home:
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.
Don’t take an FOBT during your period — this can cause a false positive. Also, avoid taking this test if you have:
You can go back to your routine after completing the FOBT. You’ll probably have to wait at least a week for the results.
There are no known risks or side effects associated with the FOBT.
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.
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.
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.
Last reviewed by a Cleveland Clinic medical professional on 09/30/2022.
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