Overview of Fecal Occult Blood Test (FOBT)

A Non-Invasive Way to Check for Blood in the Stools

Lab technician with blood samples and medical chart. Credit: Dana Neely / Getty Images

A fecal occult blood test (FOBT) is a non-invasive way to screen for blood in your stools, which can be a symptom of colon cancer. If a FOBT finds blood in your stools, you will be referred for further colon cancer screening, such as colonoscopy or flexible sigmoidoscopy.

What is a Fecal Occult Blood Test

For the fecal occult blood test (FOBT), you collect several stool samples and then ship these samples to a laboratory to be tested for the presence of blood.

Your doctor will provide you with the kit to collect your stool samples or will tell you where you can purchase the kit for yourself.

How Do You Prepare for a FOBT?

The FOBT is a test that looks for blood in your stools. Blood in your stools may indicate the presence of colon cancer. You collect stool samples in your home and then send them to a lab to be analyzed for the presence of blood.

To prepare for this test, you will be instructed to avoid certain foods and medications for several days before you collect stool samples.

Some medications, such as aspirin or ibuprofen, can cause bleeding in your stomach or intestines, which may cause a false positive on your test. A false positive means that the test will show you have colon cancer even if you don’t. Some foods, such as red meat, also can cause false positives on the FOBT.

Vitamin C supplements may create the opposite problem—they can cause a false negative.

A false negative means the test will show you do not have colon cancer, when in fact you do.

What Happens During the Test?

Your doctor will tell you where to purchase a FOBT kit or will provide you with the kit, which will include instructions on how to collect your stool samples. Below is a general description of how you will collect samples, but be sure to follow the instructions in your kit exactly.

You will use a dry container from the kit to collect your bowel movement before it goes into the toilet bowl or mixes with urine. Your kit will contain a wooden spatula or brush that you can use to collect a small amount of stool from a couple of different areas of the bowel movement. You then smear the stool on a card and store it in an envelope overnight to dry. Then you can flush the rest of the bowel movement down the toilet.

You will follow this same process for the next two bowel movements you have. Once you have collected your samples from three consecutive bowel movements, you will ship them to a lab to be analyzed for the presence of blood.

What Happens Next?

If the lab tests of your stool samples test positive for blood, you will need a sigmoidoscopy or colonoscopy to follow up.

What are the Possible Complications of the FOBT?

There are no complications of the FOBT.

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