Fecal occult blood test (FOBT)
The Fecal Occult Blood Test (FOBT) is a screening tool used primarily to detect hidden blood in the stool, which can be an early indicator of gastrointestinal cancers, including colorectal cancer. This test is particularly important because early-stage cancer may not present any symptoms, making screening essential. The FOBT works by analyzing stool samples for blood that may come from benign or malignant polyps, tumors, or other gastrointestinal disorders.
Preparation for the test requires patients to avoid certain foods and medications that may lead to false-positive results. During the test, small stool samples are collected and placed on a test card, where a chemical solution is added; a color change indicates the presence of blood. Although FOBT is generally safe and non-invasive, it is important to note that a positive result does not confirm cancer but rather indicates the need for further investigation.
Annual screening is recommended for adults starting at age fifty, though those with specific risk factors may need to be screened earlier. Additionally, newer immunochemical versions of the test have been developed that require less dietary restriction and improve the accuracy of results. Regular checkups remain crucial, regardless of FOBT outcomes, to ensure comprehensive health monitoring.
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Fecal occult blood test (FOBT)
Also known as: Stool occult blood, guaiac smear test
Definition:A fecal occult blood test (FOBT) is a simple chemical test on stool (feces) that detects the iron-containing components of hidden or trace amounts of blood. It tests for digestive tract bleeding, a possible indicator of colorectal cancer.
Cancers diagnosed: Colon (large intestine) cancer, rectal cancer, gastric (stomach) cancer
Why performed: Sometimes hidden blood in the stool is the only sign of cancer in its early stages, before symptoms appear. As a result, the FOBT is most frequently used as a colorectal cancer screening test.
Benign (noncancerous) and malignant (cancerous) polyps, tumors, and other tissues that protrude into the intestine can bleed intermittently. The FOBT can detect this abnormal bleeding. It does not diagnose disease. It screens for bleeding that may be caused by gastrointestinal cancer.
Other maladies cause blood loss in the digestive tract and anemia, a low red blood cell count. Therefore, the FOBT is sometimes used to determine the cause of unexplained anemia. It is also used to find the cause of abdominal pain.
Normally, a small amount of blood, a quarter of a teaspoonful or less, leaves digestive tract blood vessels daily and moves into the stool. The FOBT does not react to this small amount of blood. A daily blood loss of at least ten milliliters, or two teaspoonfuls, is required to produce a positive test.
Patient preparation: People who prepare for the FOBT pay attention to their health conditions. They avoid the FOBT when their other situations cause digestive or urinary bleeding, which can produce false positive results. Interfering conditions include anal fissures, gum bleeding after dental procedures, colitis, constipation, diverticulitis, esophagitis, gastroesophageal reflux disease (GERD), gastritis, hemorrhoids, inflammatory bowel disease, menstrual periods, nosebleeds, peptic ulcers, severe throat irritation, and urinary tract infections.
Before FOBT testing, patients restrict certain food, medications, and dietary supplements that can interfere with the test by producing misleading results. They should avoid the following foods for two to three days before the test to prevent false positive results: red meats such as beef, cold cuts, lamb, liver, and processed meats; fish; fruits such as apples, oranges, bananas, grapefruit, grapes, lemons, and melons; poultry; and vegetables such as beets, broccoli, cabbage, carrots, cauliflower, cucumbers, horseradish, mushrooms, radishes, and turnips.
Patients should stop taking the following medications for seven days before the test to prevent false positive results: aspirin and products that contain aspirin; other nonsteriodal anti-inflammatory drugs (NSAIDS), such as ibuprofen and naproxen; colchicine gout drugs; corticosteroids; oxidizing drugs, such as iodine, bromides, and boric acid; and reserpine.
Patients should stop taking dietary iron supplements for seven days before the test to prevent false positive results and should take no more than 250 milligrams of vitamin C per day to prevent false negative results.
Steps of the procedure: Medical facility personnel perform FOBT tests, and patients can do their own testing at home. The manufacturer’s instructions must be followed to ensure accurate testing.
A small sample of stool is placed onto a chemically treated test card, pad, or wipe. A chemical solution is added to the sample. The appearance of a blue color indicates a positive result blood in the stool sample. Absence of blue color indicates a negative result no blood in the stool sample. In one commonly used test, three stool samples are collected on three-part cards over three days, to better detect intermittent bleeding. The collection cards, pads, or wipes must be protected from heat, light, and chemicals during the collection period.
The American Cancer Society and other medical organizations recommend an annual screening FOBT for all adults beginning at age fifty. They also recommend that others have the test as needed because of personal or family histories of intestinal polyps or colorectal cancer. These organizations emphasize that negative FOBT tests do not replace regular medical checkups, and they recommend regular medical examinations for everyone.
In 2001, immunochemical fecal occult blood test (iFOBTs) became available for detecting blood in the stool. They test for a globelike protein component of blood instead of the iron-containing component detected in the traditional FOBT. They are sensitive and specific for digestive tract bleeding, and they avoid direct stool handling. These new tests have the advantage of eliminating the need to avoid foods, medications, and supplements before testing.
After the procedure: People who receive positive FOBT results have blood in the stool. They undergo specific follow-up testing, such as sigmoidoscopy, colonoscopy, computed tomography (CT) scans, and X rays, to determine the cause. People who receive negative FOBT results follow medical professionals' recommendations for regular cancer screening.
Risks: The FOBT is safe and painless and does not cause physical harm, but it is not a foolproof indicator of cancer. Digestive tract bleeding can be intermittent, and negative results can occur in people who have colorectal cancer.
Results: A normal FOBT result is negative, which means that blood is not present in the tested stool sample. An abnormal test result is positive, which means that blood is present in the tested stool sample. Occult blood appears in the stool because of colorectal cancer or other medical conditions. It is important to determine the cause and source of bleeding to diagnose, treat, and resolve the situation.
Bibliography
"Fecal Occult Blood Test." Mount Sinai Hospital. Mount Sinai Hospital, Feb. 2015. Web. 30 Nov. 2015.
Fishbach, Frances Talaska, and Marshall Barnett Dunning III. A Manual of Laboratory Diagnostic Testing. 8th ed. Philadelphia: Lippincott, 2009. Print.
Pagana, Kathleen Deska, and Timothy J. Pagana. Mosby’s Manual of Diagnostic and Laboratory Tests. 5th ed. St. Louis: Mosby, 2014. Print.
Segen, Joseph C., and Joseph Stauffer. The Patient’s Guide to Medical Tests. New York: Facts On File, 1997. Print.