A fecal occult blood tests examine the blood in the stool sample or feces. In the digestive tract, it may be a symptom of an underlying disease, such as a growth of polyp or cancer in the colon or rectum.

It’s critical for the doctor to identify the cause of bleeding to diagnose and treat the issue if the findings indicate there is blood (whether you can see it or not).

What causes blood to appear in the stool sample?

  • Growth of polyps
  • Hemorrhoids
  • Anal fissures
  • Intestinal infections that cause inflammation
  • Ulcers
  • Ulcerative colitis
  • Crohn’s disease
  • Diverticular disease
  • Problems in the blood vessels of the colon
  • Meckel’s diverticulum


  • Guaiac smear technique (gFOBT). In a stool sample, the stool guaiac test screens for hidden (occult) blood. Even if it’s not visible to the naked eyes, it can find blood. It is the most common type of FOBT. Guaiac is a plant material that is used to coat FOBT test cards.
  • Immunochemical procedure (iFOBT or FIT). The iFOBT is a colon cancer screening test. It checks for blood in the stool that is hidden, which may be an early indication of cancer. Only human blood from the lower intestines is detected by iFOBT or FIT.


You don’t have to “cleanse” the colon, as you might have done during a colonoscopy, although you do need to closely observe the directions.

Don’t take the test if you have the following:

  • Diarrhea
  • Colitis
  • Constipation
  • Diverticulitis
  • Ulcers
  • Hemorrhoid flare-ups
  • Menstruation

Don’t eat these foods for 48 to 72 hours before taking the test, it can alter the result

  • Beets
  • Broccoli
  • Cantaloupe
  • Carrots
  • Cauliflower
  • Cucumbers
  • Grapefruit
  • Horseradish
  • Mushrooms
  • Radishes
  • Rare red meat
  • Turnips
  • Vitamin C rich foods or beverages


A positive result means that it showed blood in the stool. Additional tests are then needed in order to find out where the blood came from.

The attending physician may recommend a colonoscopy, and an upper endoscopy of the urinary tract to see whether the blood is from the stomach or small intestine. The patient will then need to ingest a small capsule that takes images while it moves through the intestines if they don’t reveal the source.

Negative test findings indicate that during the testing process, no blood was detected in the stool sample.

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