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Fecal occult blood test (FOBT)

Contents of this page:

Illustrations

Fecal occult blood test
Fecal occult blood test

Alternative Names    Return to top

Stool occult blood test

Definition    Return to top

A fecal occult blood test (FOBT) is a noninvasive test (nothing enters the body). This test detects hidden (occult) blood in the stool. Such blood may come from anywhere along the digestive tract. Hidden blood in stool is often the first, and in many cases the only, warning sign that a person has colorectal disease, including colon cancer.

How the Test is Performed    Return to top

There are two types of FOBTs: 1) the traditional guaiac smear test (Hemoccult, Seracult, Coloscreen), and 2) the newer, flushable reagent pads (EZ DetectT, ColoCARE). They are both useful in detecting hidden blood in the stool, and are mainly used for colorectal cancer screening.

The tests differ in the way they are performed. The flushable reagent pads are available without a prescription at many drugstores. In contrast, the traditional guaiac smear test is completed and interpreted by a medical professional, and these tests are usually available from a laboratory or a doctor's office.

Many consumers prefer the flushable reagent pads because there is no stool handling and no laboratory processing. However, health care providers usually favor the guaiac tests because the large studies that have shown the benefits of colon cancer screening were done with guaiac tests.

See description under specific type of FOBT for how these tests are performed.

How to Prepare for the Test    Return to top

See description under specific type of FOBT.

How the Test Will Feel    Return to top

See description under specific type of FOBT.

Why the Test is Performed    Return to top

This test is mainly performed yearly for colorectal cancer screening. It may also be performed in the evaluation of anemia.

Advantages:

Disadvantages:

Normal Results    Return to top

A "negative" test result is normal. It means no blood was found in the stool.

What Abnormal Results Mean    Return to top

Positive test results may indicate the following:

Note that false positives are common.

Additional conditions under which the test may be performed include the following:

Risks    Return to top

A negative test does not necessarily mean there are no colorectal diseases present. Not all polyps bleed, and not all polyps bleed all the time. That is why a FOBT must be used with one of the other more invasive screening measures (sigmoidoscopy, colonoscopy, double barium contrast enema).

Considerations    Return to top

Colonoscopy is generally recommended as the preferred follow-up test to a positive FOBT.

Factors that can cause this test to be less accurate include the following:

Drugs that can cause GI bleeding include anticoagulants, aspirin, colchicine, iron supplements in large doses, NSAIDs (anti-inflammatory analgesics), and corticosteroids.

Drugs that can cause false positive measurements include colchicine, iron, oxidizing drugs (for example, iodine, bromides, and boric acid), and reserpine.

Large amounts of vitamin C can cause false-negative results on most FOBTs.

In general, avoiding food is not recommended, with the exception of red meat as described above.

References    Return to top

Atkins D. The periodic health examination. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, PA: Saunders Elsevier; 2008:chap 13.

Update Date: 3/8/2008

Updated by: Christian Stone, MD, Division of Gastroenterology, Washington University in St. Louis School of Medicine, St. Louis, MO. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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