Fecal Occult Blood Test (FOBT)

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.

Why this test is done

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.

How to prepare

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.

Sample type

Blood Stool

Other names for this test

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