Fecal Occult Blood Test

A lab test used to check stool samples for hidden blood is called fecal occult blood test (FOBT).

If you have an occult blood in your stool it may indicate colon cancer or polyps in the rectum or colon.

Occult blood can only be detected through the chemicals used in a fecal occult blood test because this is passed in such small amounts.

Additional test may be needed to determine the source of bleeding if blood is detected through a fecal occult blood test.

This test does not indicate potential sources of bleeding because it can only detect the absence or presence of blood.

Here are the most common reasons to undergo a fecal occult blood test.

Your doctor may suggest this test to:

Evaluate possible causes of unexplained anemia – to determine if bleeding in your digestive tract (bleeding ulcer) is contributing to anemia – a condition where there are no enough healthy blood cells to carry oxygen to your tissue.

Screen for colon cancer – this is recommended if you are 50 years old and older and you may need other tests along with these.

The possible risks of having a fecal occult blood test are:

The test is not always accurate – your test could show a positive result when you have no cancer (false-positive result) if you have to bleed from other sources such as hemorrhoid, stomach ulcer or blood swallowed from your nose or mouth.

Or it will show negative test result when cancer is present (false-negative result) if your polyps or cancer does not bleed.

Having this test may lead to another additional testing – your doctor may suggest further observation and evaluation of your upper gastrointestinal tract if the result is positive but follow-up colonoscopy is normal.

This test cannot detect all cancers – in some cases. Cancer may be detected in colonoscopy but not in a fecal occult blood test.

In preparing for your fecal occult blood tests, you must follow your doctor’s orders. 

The results of some of the fecal occult blood tests may be affected because of foods, medications, and dietary supplement, even if it is indicating false-positive or false-negative.

Your doctor may give you restrictions in food or medicines. Follow your doctor’s instructions so that the results will be accurate.

Your doctor may ask you to avoid these for about three days before the test:

• red meat
• vitamin C supplements
• certain vegetables and fruits such as turnips and broccoli
• horseradish
• pain relievers such as ibuprofen (Advil, Motrin IB) and aspirin

Here you can find out what to expect from your fecal occult blood tests.

Some of the types of fecal occult blood test wit different approach include:

Guaiac fecal occult blood test (gFOBT) – your doctor will give you two or three test cards or two or three samples and you will collect a stool sample in a clean container from each of two to three bowel movements (mostly taken on consecutive days), and then you will be given an applicator stick to apply a smear of stool to a specific area of the card. Once they are dried you will return them to your doctor.

Flushable reagent pad or tissue – this kit is available at a store and you will not need any prescription. This pad will be placed in the toilet bowl after a bowel movement and if the pad changes color, there is blood present.

Contact your doctor after you get the results; immunochemical fecal occult blood test (iFOBT or FIT) – mostly you will use a special spoon or some devices to collect a stool sample that will be placed in a clean container.

You will then give the container to your doctor and this does not need any dietary restrictions before getting the sample and you can get the stool samples randomly but this is more sensitive than gFOBT.

You and your doctor will talk about the results of your fecal occult blood test.

A positive result means that blood is detected in the stool samples and you may need further testing such as colonoscopy to check where the bleeding is coming from.

A negative result means there is no blood in your stool sample but if you had this test to check for colon cancer, your doctor may suggest that you should wait for another year to repeat the test.