Fecal Occult Blood Test (FOBT)

What is a fecal occult blood test?

A fecal occult blood test (FOBT) checks for blood in a sample of your stool (poop). It's called occult (hidden) blood because you can't see it just by looking at it. And fecal means that it is in your stool.

Blood in your stool means there is bleeding in the digestive tract. The bleeding can be caused by a variety of conditions, including:

• Polyps, abnormal growths on the lining of your colon or rectum
• Hemorrhoids, swollen veins in your anus or rectum
• Diverticulosis, a condition in which you have small pouches in the inside wall of your colon
• Ulcers, sores in the lining of your digestive tract
• Ulcerative colitis, a type of inflammatory bowel disease
• Colorectal cancer, a type of cancer that starts in your colon or rectum

Colorectal cancer is one of the most common types of cancer in the United States. A fecal occult blood test can screen for colorectal cancer to help find the disease early, when treatment may be most effective.

Other names: FOBT, stool occult blood, occult blood test, Hemoccult test, guaiac smear test, gFOBT, immunochemical FOBT, iFOBT; FIT

What is it used for?

A fecal occult blood test is commonly used as a screening test to help find colorectal cancer before you have symptoms. The test may also be used to check for other conditions that can cause gastrointestinal (GI) bleeding.

In certain cases, the test is used to help find the cause of anemia. It can also help tell the difference between irritable bowel syndrome (IBS), which usually doesn't cause bleeding, and inflammatory bowel disease (IBD), which is likely to cause bleeding.

But a fecal occult blood test alone cannot diagnose any condition. If your test results show blood in your stool, you will likely need other tests to find the exact cause.

Why do I need a fecal occult blood test?

Your health care provider may order a fecal occult blood test if you have symptoms of a condition that could involve bleeding in your digestive tract. Or you may have the test to screen for colorectal cancer when you don't have any symptoms.

Regular screening tests for colorectal cancer can detect colon polyps and colorectal cancer. If you aren't at higher risk for colorectal cancer, your provider will likely recommend you start screenings at age 45. If you are at higher risk, you may need to start getting screened for colorectal cancer earlier. Talk with your provider about when to start, how often to get screened, and which type of test you should have.

A fecal occult blood test is one of several types of colorectal screening tests. Other tests include:

• A stool DNA test (FIT-DNA test). This test checks for genetic changes in your stool that may be signs of colorectal polyps or cancer.
• Colonoscopy or sigmoidoscopy. Both tests use a thin tube with a camera to look inside your colon. A colonoscopy allows your provider to see your entire colon. A sigmoidoscopy shows only the lower part of your colon.
• CT colonography, also called "virtual colonoscopy." For this test, you usually drink a liquid containing contrast dye before having a CT scan. The CT scan uses x-rays to take detailed 3-dimensional pictures of your entire colon and rectum. The contrast dye makes your colon and rectum show up more clearly on the x-rays.

Each type of test has pros and cons. Your provider can help you decide which test is right for you.

What happens during a fecal occult blood test?

Usually, your provider will give you a kit to collect samples of your stool (poop) at home. The kit will include instructions on how to do the test.

There are two main types of fecal occult blood tests:

• The guaiac fecal occult blood test (gFOBT) uses a chemical (guaiac) to find blood in stool. It usually requires stool samples from two or three separate bowel movements.
• The fecal immunochemical test (iFOBT or FIT) uses an antibody, a type of protein that attaches to hemoglobin (blood) in stool. FIT is considered better at finding blood in your stool than gFOBT testing. A FIT test requires stool samples from one to three separate bowel movements, depending on the brand of the test.

Different test kits have different instructions, so it's very important to follow the specific instructions that come with your kit. The typical process for gathering a stool sample usually includes these general steps:

• Collecting a bowel movement. Your kit may include special paper to place over your toilet to catch your bowel movement. You may also use plastic wrap or a clean, dry container. If you are doing a guaiac test, be careful not to let any urine mix in with your stool.
• Taking a stool sample from the bowel movement. Your kit will include a wooden stick or applicator brush for scraping the stool sample from your bowel movement. Follow the instructions for where to gather the sample from the stool.
• Preparing the stool sample. You will either smear the stool on a special test card or insert the applicator with the stool sample into a tube that came with your kit.
• Labeling and sealing the sample as directed.
• Repeating the test on your next bowel movement as directed if more than one sample is needed.
• Returning the samples as directed. This might be mailing them or taking them to your provider's office or a lab.

Will I need to do anything to prepare for the test?

You do not need any special preparations for many fecal occult blood tests. But for some guaiac fecal occult blood tests (gFOBTs), certain foods, supplements, and medicines may affect the results of the test. If you are having one of these tests, your provider will tell you what you need to avoid and for how long. For example, you might need to avoid:

• Nonsteroidal, anti-inflammatory drugs (NSAIDs), such as ibuprofen, naproxen, and aspirin. If you take aspirin for heart problems, talk with your provider before stopping your medicine. You may be able to take acetaminophen during this time, but check with your provider before taking it.
• Vitamin C in amounts over 250 mg a day. This includes vitamin C from supplements, fruit juices, or fruit.
• Red meat, such as beef, lamb, and liver. Traces of blood from these meats may show up in your stool.
• Certain raw fruits and vegetables.

Are there any risks to the test?

There is no known risk to having a fecal occult blood test.

What do the results mean?

If your results from a fecal occult blood test show that you have blood in your stool, it means you likely have bleeding somewhere in your digestive tract. But that doesn't always mean you have cancer. Other conditions that may cause blood in your stool include ulcers, hemorrhoids, polyps, and benign (not cancer) tumors.

If you have blood in your stool, your provider will likely recommend more tests to figure out the exact location and cause of your bleeding. The most common follow-up test is a colonoscopy. If you have questions about your test results, talk with your provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a fecal occult blood test?

Regular colorectal cancer screenings, such as fecal occult blood tests, are an important tool in the fight against cancer. Studies show that screening tests can help find cancer early and may reduce deaths from the disease.

If you decide to use fecal occult blood testing for your colorectal cancer screening, you will need to do the test every year.

You can buy gFOBT and FIT stool collection kits without a prescription. Most of these tests require you to send a sample of your stool to a lab. But some tests can be done completely at home for quick results. If you're considering buying your own test, ask your provider which one is best for you.