Colorectal Cancer Screening: Testing for Blood in Your Stool

There are several ways to check for colorectal cancer, and testing for blood in your stool is one of them. These tests can detect signs of colorectal cancer or polyps because sometimes colorectal cancers or polyps bleed into your digestive tract. This blood can then go into your stool or feces. While these tests might sound uncomfortable, there is some good news. They can be done in the comfort of your own home.

What tests are available?

There are 2 main types of tests. They include:

  • Guaiac fecal occult blood test (gFOBT). This uses a chemical to find blood in your stool.

  • Fecal immunochemical test (FIT). This looks for blood in the stool that comes from your lower intestines.

What do I need to know about the tests?

Before you get started, here are some things to know.

  • If you're using one of these tests to screen for colorectal cancer, it must be done every year.

  • These screening tests don’t find cancer. They look for blood in your digestive tract.

  • If the test finds blood in your stool, it doesn’t mean that you have cancer. It could mean that you have polyps, hemorrhoids, diverticulosis, or inflammatory bowel disease. Talk with your healthcare provider after your results to know for sure.

  • It’s possible to have false positives and false negatives. A false positive is when the test shows the possibility of a polyp or cancer when it’s not there. A false negative is when the test doesn’t show cancer or a polyp since it doesn't bleed.

  • If your result is positive, you will need a colonoscopy to look for the cause of the bleeding. Talk with your provider about next steps. They can help you schedule a colonoscopy.

How do I perform the tests?

Luckily, you don’t need to go to a lab to get these tests done. They’re easy to do on your own from home. Your healthcare provider can give you a test kit and any additional information you may need. While these tests are simple, know that they do involve collecting your own stool (poop).

Each test has different instructions, so it's very important to follow them exactly for accurate results. When you’re about to do the test, check that you have all your supplies nearby in the bathroom.

You may need to collect 1 to 3 separate stool samples depending on the type of test. You can gather the stool using a clean container or by draping plastic wrap loosely across your toilet bowl to catch it. Then, use the provided applicator to spread the sample onto the testing kits before sending them as instructed.

Do I need to prep?

The American Cancer Society and U.S. Preventive Services Task Force advise people at an average risk for colorectal cancer start screening at age 45. You may need to start screening earlier if you’re at a higher risk. Your provider can help you determine this.


If you’re using the FIT, you’re in luck. There aren’t any dietary or medicine restrictions for taking the test. Medicines and foods don’t affect this test.


You need to pay close attention to your eating and other habits if you’re using the gFOBT. Don’t forget that it’s very important to follow the prep instructions in your kit to make sure you get the correct results.

All test kits come with detailed instructions. But certain foods and medicines can affect the results of gFOBT tests. So you might see these general guidelines:

  • Don't eat red meat (beef, liver, or lamb) for 3 days before the test.

  • Don't have more than 250 mg of vitamin C a day (either from supplements or citrus fruits and juices) for 3 to 7 days before the test.

  • Don't use products that contain aspirin or use nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and naproxen, for 7 days before the test.

Always read the prep kit thoroughly before you test. If you have questions, talk with your healthcare provider. They’re there to help you through the testing process so you’re comfortable doing it at home.

Online Medical Reviewer: Jessica Gotwals RN BSN MPH
Online Medical Reviewer: Sabrina Felson MD
Online Medical Reviewer: Todd Gersten MD
Date Last Reviewed: 5/1/2023
© 2024 The StayWell Company, LLC. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare provider's instructions.