Fecal Occult Blood Test


What is a Fecal Occult Blood Test?

The fecal occult blood test (FOBT) is a type of screening that could indicate colorectal cancer but not diagnose it. A fecal occult blood test checks for blood in the stool which cannot be seen with the naked eye. If blood is detected, additional testing would be required to determine the source of the blood. Fecal occult blood testing is what is known as a qualitative test. It only detects the presence or absence of blood. If blood is present, the test cannot evaluate how much blood is in the stool.


A fecal occult blood test may be a good option for a colon cancer screening. If you are age 50 or older, your doctor may recommend this screening once per year. You may, however, need other screenings that directly examine the colon. Fecal occult blood testing can also reflect many other gastrointestinal conditions which cause blood in the stool.

Preparing for the FOBT

It is important that you are prepared for a fecal occult blood test and ask your doctor all your questions before you begin. Many factors can interfere with a fecal occult blood test, since it only evaluates the presence of blood in the stool. Blood from any other source like a bleeding hemorrhoid or a menstrual period may produce a positive result.

Your doctor will also give you a list of foods, dietary supplements and medications to avoid before the fecal occult blood test. A few of these may include:

  • Red meat—you may have fish or poultry, but red meat can make your stool to appear to have blood even when it does not.
  • Certain fruits and vegetables like broccoli, beets, radishes, horseradish, turnips, grapefruit, cantaloupe and carrots may also make it appear that you have blood in your stool.
  • Vitamin C supplements, aspirin and ibuprofen—stop taking these at least seven days before the test, as they can give a false positive result.

Types of Fecal Occult Blood Tests

Although the methods are slightly different, all fecal occult blood tests have the same objective: to detect blood in the stool. Several samples are taken in a fecal occult blood test because polyps and abnormalities do not bleed every day. There is less of a chance for error when doctors and laboratories view samples over the course of consecutive days.

Flushable reagent pad or tissue

This over-the-counter test kit can be purchased at a store. For three consecutive days, you place the pad in the toilet bowl after a bowel movement. If blood is detected in the stool, the pads will change in color. You send the results to your doctor using a mail-in form.

Guaiac Fecal Occult Blood Test (gFOBT)

Your doctor will give you a test card that has room for several samples. You will collect a stool sample from two or three bowel movements on consecutive days in a clean container. You will then use an applicator to put a small sample of stool on a specific area of the card. When the samples dry, you will return them to your doctor or a laboratory.

Immunochemical Fecal Occult Blood Test (iFOBT or FIT)

This is a more sensitive test than gFOBT, and it does not require dietary restrictions before collecting a sample. The test itself requires less effort because it involves simply brushing the surface of the stool in the toilet water and dabbing the brush on a test card.

What Happens After the FOBT

Your doctor will review your test results and notify you.

A negative test indicates that there is no blood detected in the stool samples. If the primary reason for the fecal occult blood test was a colon cancer screening and you are at average risk, your doctor may recommend repeating the test after one year.

A positive test means that blood was detected in your stool samples. Your doctor will recommend further testing to determine the source of the bleeding. Often, the next step is a colonoscopy.

What Does a Positive Result Mean?

Blood in the stool is one sign of colorectal cancer, but it does not always mean cancer. The presence of blood could indicate many other conditions such as:

  • Hemorrhoids
  • Colon polyps
  • Peptic ulcers
  • Anal fissures
  • Ulcerative colitis and Crohn’s disease
  • Recent use of aspirin or nonsteroidal anti-inflammatory drugs

Fecal occult blood testing is never used to diagnose colon cancer. It is, however, an inexpensive test that can detect blood in the stool. If blood is detected, you will need to have another test that examines the colon directly, such as a colonoscopy, flexible sigmoidoscopy or virtual colonoscopy.

A colonoscopy is the most comprehensive colon screening because it both diagnoses colon cancer and removes cancerous growths. Talk to your doctor about what screening method is best for you. Each individual has unique screening needs when considering age, risk factors, family history and personal history. Colonoscopy is the gold standard for colon screening, so talk to your doctor and insurance provider about benefits and coverage so that you can obtain the most thorough colon screening.