The fecal occult blood test (FOBT) is a lab test used to check stool samples for hidden (occult) blood. Occult blood in the stool may indicate colon cancer or polyps in the colon or rectum though not all cancers or polyps bleed. Typically, occult blood is passed in such small amounts that it can be detected only through the chemicals used in a fecal occult blood test.
Stool analysis is done to:
- Help identify diseases of the digestive tract, liver, and pancreas. Certain enzymes (such as trypsin or elastase) may be evaluated in the stool to help determine how well the pancreas is functioning.
- Help find the cause of symptoms affecting the digestive tract, including prolonged diarrhea, bloody diarrhea, an increased amount of gas, nausea, vomiting, loss of appetite, bloating, abdominal pain and cramping, and fever.
- Screen for colon cancer by checking for hidden (occult) blood.
A stool analysis is a series of tests done on a stool (feces) sample to help diagnose certain conditions affecting the digestive tract. These conditions can include infection (such as from parasites, viruses, or bacteria), poor nutrient absorption, or cancer.
Screen for colon cancer. If you’re age 50 or older and at average risk of colon cancer, your doctor may recommend a fecal occult blood test every year to screen for colon cancer. In addition, however, you may need other screening tests that allow the doctor to examine the colon directly. Evaluate possible causes of unexplained anemia. Anemia is a condition in which there aren’t enough healthy red blood cells to carry adequate oxygen to your tissues. Sometimes a fecal occult blood test is used to determine whether bleeding in your digestive tract such as a bleeding ulcer is contributing to anemia.
How to Identify?
Many medicines can change the results of this test. You will need to avoid certain medicines depending on which kind of stool analysis you have. You may need to stop taking medicines such as antacids, antidiarrheal medicines, antiparasite medicines, antibiotics, laxatives, or nonsteroidal anti-inflammatory drugs (NSAIDs) for 1 to 2 weeks before you have the test. Be sure to tell your doctor about all the nonprescription and prescription medicines you take.
There are several types of fecal occult blood tests, each with a different approach to collecting and testing stool.
- Guaiac fecal occult blood test (gFOBT).
- Flushable reagent pad or tissue.
- Immunochemical fecal occult blood test (iFOBT, or FIT).
What to Do?
- Negative result. A fecal occult blood test is considered negative if no blood is detected in your stool samples. If you had the test to screen for colon cancer and you’re at average risk you have no colon cancer risk factors other than age your doctor may recommend waiting one year and then repeating the test.
- Positive result. A fecal occult blood test is considered positive if blood is detected in your stool samples. You may need additional testing such as a colonoscopy to locate the source of the bleeding.