Fecal Occult Blood Test

This is a test done on a stool specimen to screen for gastrointestinal bleeding, which may be an indicator of colon cancer Is is usually done as part of a routine examination, annually, after age 50 or as directed by your caregiver.

The fecal occult blood test (FOBT) checks for blood in your stool. Normally, there will not be enough blood lost through the gastrointestinal tract to turn an FOBT positive or for you to notice it visually in the form of bloody or dark, tarry stools. Any significant amount of blood being passed should be investigated.

A positive FOBT will tell your caregiver that you have bleeding occurring somewhere in your gastrointestinal tract. This blood loss could be due to ulcers, diverticulosis, bleeding polyps, inflammatory bowel disease, hemorrhoids, from swallowed blood due to bleeding gums or nosebleeds, or it could be due to benign or cancerous tumors. Anything that protrudes into the lumen (the empty space in the intestine), like a polyp or tumor, and is rubbed against by the fecal waste as it passes through has the potential to eventually bleed intermittently. Often this small amount of blood is the first, and sometimes the only, symptom of early colon cancer, making the FOBT a valuable screening tool.


You should not eat red meat within three days before testing. Other substances that could cause a false positive test result include fish, turnips, horseradish, and drugs such as colchicines and oxidizing drugs (for example, iodine and boric acid). Be sure to carefully follow your caregiver's instructions.

With FOBT, your caregiver or laboratory will give you one or more test "cards." You collect a separate sample from three different stools, usually on consecutive days. Each stool sample should be collected into a clean container and should not be contaminated with urine or water. The slide is labeled with your name and the date; then, with an applicator stick, you apply a thin smear of stool onto each filter paper square/window contained on the card. Allow the filter paper to dry. Once it is dry, it is stable. Usually you will collect all of the consecutive samples, and then return all of them to your caregiver or laboratory at the same time, sometimes by mailing them. There are also over the counter tests which are dropped in your toilet.


  • No occult blood within the stool.

  • The FOBT test is normally negative. A positive indicates either blood in the stool or an interfering substance. Multiple samples are done to: 1) catch intermittent bleeding; and 2) help rule out false positives.

Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.


Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.


It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.