Fecal Occult Blood Test
Fecal Occult Blood Testing with a Smear Test
A fecal occult blood test (FOBT) checks for blood that may be hidden in a patient’s stool. The source of the blood can be anywhere along the gastrointestinal (GI tract), from stomach ulcers to colon cancer. Although blood in the stool is not always cause for concern, persistent or unexplainable bleeding is oftentimes an early symptom of colon cancer or other GI diseases. Experts recommend that the test should be taken once every 1-2 years in patients over 50 years old, and used in combination with sigmoidoscopy or colonoscopy. There are newer methods of stool blood testing such as Fecal Immunohistochemical Testing (FIT) which has mostly replaced this test as the stool test of choice for screening of colorectal cancer.
Bowel prep is unnecessary before a fecal occult blood test, but patients are usually asked to practice some dietary restrictions in the days before a procedure, such as avoiding red meat and other food products high in iron that can make the stool appear abnormally dark. The most common type of fecal occult blood test is a smear test. During a traditional smear test, a sample of the patient’s stool is placed on a card that has been soaked in reactive, chemical substances. A lab technician will then put another chemical solution on top of the sample, making sure that it touches both the fecal matter and the chemical card material. If the material on the card turns blue, then it means that there is blood in that stool sample.
Garnering positive or abnormal results from a fecal occult blood test can mean a number of different things. It may be possible that the patient has an underlying gastrointestinal condition that is causing internal bleeding. Examples of such conditions include polyps or pouches along the GI tract, stomach ulcers, tumors, hemorrhoids, diverticulosis, fissures and inflammatory bowel disease (IBD).
Advantages of a Fecal Occult Blood Test
A fecal occult blood test is simple and non-invasive—so many patients find it to be a great alternative to other screening tests. Since stool samples can be taken at home, FOBT is also a way to screen for colon cancer without having to worry about a heavy financial burden. The cost of a smear test or a flushable pad is relatively low compared to the cost of other colon cancer screening procedures that may be more serious or more comprehensive. During a fecal occult blood test, there is minimal risk of damage to the colon.
Disadvantages of a Fecal Occult Blood Test
One major downside to performing a fecal occult blood test is that the results might show a patient blood in the stool, but it won’t reveal its cause. Unfortunately, the test also cannot detect the presence of most polyps, especially those located deeper inside the large intestine. It often produces false-positive results and is therefore not the keenest indicator of colon cancer. If abnormalities are detected during FOBT, then a colonoscopy or other procedure might become necessary. Also, a negative result does not exclude the possibility of colonic polyp or cancer.
Contact one of our colonoscopy specialists if you are collecting a stool sample for the first time or to contact a lab that can help interpret the results of your fecal occult blood test.
Reviewed 12/12/2011 by David M. Nolan, M.D.
Diplomate of the American Board of Internal Medicine, 2011
Currently a Fellow of Gastroenterology, at UCI 2011-2014