The fecal occult blood test is one of a variety of colorectal
cancer screening tests. When doctors test for fecal occult blood, they are
testing for the presence of microscopic or invisible blood in the stool, or
feces. Fecal occult blood can be a sign of a problem in your digestive system,
such as a growth, or polyp, or cancer in the colon or rectum. If microscopic
blood is detected, it is important for your doctor to determine the source of
bleeding to properly diagnose and treat the problem.
What causes blood to appear in stool?
Blood may appear in the stool because of one or more of the following conditions:
- Benign (non-cancerous) or malignant (cancerous) growths or polyps of the
colon
- Hemorrhoids (swollen blood vessels near the anus and lower rectum that
can rupture, causing bleeding)
- Anal fissures (splits or cracks in the lining of the anal opening)
- Intestinal infections that cause inflammation
- Ulcers
- Ulcerative colitis
- Crohn's disease
- Diverticular disease, caused by outpouchings of the colon wall
- Abnormalities of the blood vessels in the large intestine
Gastrointestinal bleeding may be microscopic (occult blood), or
may be easily seen as red blood, or black tar-like bowel movements, called
melena.
How do I take a fecal occult blood test?
The fecal occult blood test requires the collection of 3 stool
samples. The stool samples should be taken one day apart, because colon cancers
may bleed from time to time, rather than consistently.
You can purchase fecal occult blood test kits at the pharmacy to
perform the test at home, or your doctor may give you the home test during one
of your appointments. These tests provide specific instructions, and most offer
a toll-free number to call if you have questions.
The stool samples are collected in a clean container and
evaluated by detecting color changes on a test card, or by sending the samples,
in a special container and envelope, directly to the doctor’s office for
analysis. Your doctor may examine the samples with a microscope or with chemical
tests.
How should I prepare for a fecal occult blood test?
The test results are largely affected by how you prepare for the
test, so it is important to follow the instructions carefully.
Do not perform the test if you have:
- Diarrhea
- Colitis
- Constipation
- Diverticulitis
- Ulcers
- Severe throat irritation
- Hemorrhoid flare-ups
- Your period
Because certain foods can alter the test results, a special diet
is often recommended for 48 to 72 hours before the test.