Fecal occult blood testing

Description
Fecal occult blood is a small amount of blood in the stool that's not visible to the naked eye. This "hidden" bleeding in the gastrointestinal tract can often be detected with fecal occult blood testing (FOBT). Stool samples are collected at home and applied to special cards, which are sent to a lab and analyzed through chemical testing.

Indications
Fecal occult blood testing is mainly used as a screening tool for colorectal cancer or to help determine the cause of anemia (a condition marked by a decreased number of red blood cells or hemoglobin, a protein in red blood cells that contains iron).
The U.S. Preventive Services Task Force (USPSTF) strongly recommends that clinicians test average-risk people beginning at age 50 for early colorectal cancer detection. In addition, the American Cancer Society (ACS) recommends starting colorectal cancer screening for average-risk people at age 50.

To detect colorectal cancer in its early stages, here are some options:

routine at-home fecal occult blood testing (The USPSTF recommends at-home testing every one to two years. The ACS recommends yearly testing.)
flexible sigmoidoscopy every three to five years
a combination of at-home fecal occult blood testing and flexible sigmoidoscopy
colonoscopy every 10 years
double-contrast barium enema every five years
The ACS recommends the combination of at-home fecal occult blood testing and flexible sigmoidoscopy as the most effective. The USPSTF has not recommended one method over the others.

If you're at high risk for colorectal cancer, you may need earlier screening. Some factors that may increase your risk for developing colorectal cancer include:

a diet high in fat and calories and low in fiber
a personal or close family history of colon cancer or polyps (growths) in the colon
inflammatory bowel disease, such as ulcerative colitis or Crohn's disease
a history of uterine, ovarian or breast cancer
Ask your doctor about the best screening schedule based on your family and personal medical history.


Patient preparation
For the most accurate test results, it's important to carefully follow your doctor's instructions on how to use the kit. Test results can be affected by various factors.
Diet
For up to three days before the test and until it's completed, you may be asked to eat cooked fruits and vegetables and high-fiber foods, such as whole-wheat bread, bran cereal and popcorn. You may be asked to avoid red meat (including processed meat and liver), fish and some raw fruits and vegetables (such as melons, radishes, turnips and horseradish). If recommended, these dietary changes can help you obtain adequate stool samples, as well as reduce the potential for false results.

Medications and vitamins
Some medications and vitamins can interfere with fecal occult blood test results. For example, your doctor may ask you to avoid the following medications for several days before and during the test:

colchicine (used to treat or prevent gout)
oxidizing drugs, such as iodine, bromides and boric acid (sometimes used to prevent or treat infections)
topical antiseptic wipes containing iodine to the anal area
rauwolfia derivatives (sometimes used to treat high blood pressure)
iron supplements
other medications as instructed by your doctor
You may also be asked to avoid taking vitamin C supplements, since excessive vitamin C can produce a false-negative result.

Certain medications can cause gastrointestinal bleeding or irritate the gastrointestinal tract, which may interfere with the test results. Your doctor may ask you to avoid:

blood thinners (anticoagulants)
aspirin
excessive amounts of alcohol
nonsteroidal anti-inflammatory drugs such as ibuprofen (Motrin or Advil, for example)
certain steroidal medications, such as prednisone
Be aware that some medications, such as steroids or some blood thinners, must only be tapered or even held upon the advice of your doctor. Do not modify doses by yourself.

Other factors
Bleeding gums after a dental procedure and recent bleeding from the nose may also interfere with test results. Consult your doctor if this may be an issue.


Procedure
When you collect your stool samples, remember to follow your doctor's instructions to prevent contamination with toilet tissue or urine. Here are a few general guidelines.
Read the directions on the test kit. Each manufacturer may have unique instructions.

Check the expiration date on the package before using the test kit. Do not use an outdated kit. It may not be accurate.

To avoid any chemical interactions, you may want to remove toilet bowl cleaners from your toilet before collecting the samples.

Don't collect samples if you have bleeding hemorrhoids or notice blood in your urine. If you're menstruating, wait to collect the samples until at least three days after your period.

Collect the samples from three consecutive bowel movements or three bowel movements close together.

Return the samples to your doctor's office or lab as soon as possible. If you've been asked to mail the samples, use approved mailing pouches. U.S. postal regulations prohibit mailing completed cards or slides in standard paper envelopes. The manufacturer of your kit should supply the approved mailing pouches.

If your doctor gave you permission to continue taking your regular medications before collecting the sample, include the names of the medications on the lab slip when you return the samples.
Some people have difficulty or object to collecting or handling stool samples. If you're concerned or have any questions about the procedure, consult your doctor.


Benefits
Fecal occult blood testing is a simple, noninvasive, low-cost, effective screening tool for colorectal cancer. This type of cancer tends to grow slowly, so regular screening improves the chances of catching the condition at an early, curable stage. Regular testing can also help doctors diagnose other conditions that cause gastrointestinal bleeding.

Risks
Fecal occult blood testing poses no physical risks. Your preparation for the testing, certain medical conditions, diet, medications and how the samples are processed can lead to either false-positive or false-negative results. Also, nonbleeding colon problems can't be detected through fecal occult blood testing.

Considerations
As with all tests, false-positive or false-negative results can occur. A false-positive means blood was detected in the stool sample even though there really was none. If your test result is positive, it will typically be confirmed or ruled out through additional testing. Even if blood is accurately detected, remember that it doesn't necessarily indicate cancer. Other conditions or factors can cause gastrointestinal bleeding, such as hemorrhoids, diverticulosis (the presence of diverticula -- small, protruding pouches that can develop in the gastrointestinal tract) or peptic ulcers (sores that develops in the lining of the gastrointestinal tract).
A negative test result usually means no blood was found in your stool samples. Although reassuring, a negative result doesn't eliminate the possibility of cancer. Some cancers don't bleed, bleed too little to be detected, or bleed intermittently. A false-negative is also possible (not detecting blood that's really there), especially if you have too much vitamin C in your system.

Remember, test results can be affected by various factors. Always discuss the results with your doctor.