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Fecal Blood Test

A very small amount of blood can be found in normal stool. This blood is invisible to the eye. When the digestive tract's mucosa is damaged, the stool will contain larger than normal amount of blood.

There are 2 main types of test: the guaiac fecal occult blood test (gFOBT) and the immunochemical fecal occult blood test (iFOBT). The immunochemical test (iFOBT) is more accurate and is increasingly recommended by guidelines for colorectal cancer screening.

Why is this test done? This test
  • is used to detect blood in the stool that is invisible to the eye.
  • is done to help diagnose various digestive tract disorders such as colorectal cancer.
  • can help find the cause of anemia in certain situations.
How to prepare?
  • Guaiac Fecal Occult Blood Test (gFOBT): Medication and food restrictions may be recommended before collecting stool samples.
  • Immunochemical Fecal Occult Blood Test (iFOBT or FIT): There are no dietary or medication restrictions before the stool collection.
  • Wait until your bleeding has stopped before testing if you are menstruating or have bleeding hemorrhoids.
  • Follow the recommendations on the instruction sheet that came with your test kit.
Target values Negative test
Associated tests If the test is positive, other exams will be done to identify the cause of the bleeding (e.g. a colonoscopy).

What does a positive result mean?

Blood in the stool can be caused by several digestive tract disorders, such as polyps, ulcers, varicose veins, intestinal inflammatory diseases, recent trauma or surgery, hemorrhoids and certain cancers.

Factors that can affect the result of the test

Certain situations can falsely affect the results of the test, such as bleeding hemorrhoids or being menstrual at the time of stool collection.

Guaiac Fecal Occult Blood Test (gFOBT)

The effect of certain medications and foods on the test result is controversial. For this reason, some test manufacturers may recommend stopping certain medications and foods a few days before collection. Drugs that are often named are:

  • Non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (e.g., Advil, Motrin) and acetylsalicylic acid (e.g., Aspirin)
  • Anticoagulants such as warfarin (e.g., Coumadin)
  • Iron supplements (e.g., Palafer)
  • Vitamin C (ascorbic acid)

What you should know before going for this test

When you go in for a blood test or any other medical exam, it's always a good idea to bring a complete list of any prescriptions, over-the-counter medications, or natural health products you're taking. Unless otherwise advised, it's best to take your medications as usual on blood test days. If in doubt, don't hesitate to talk to your healthcare professional.

© Copyright Vigilance Santé

The patient information leaflets are provided by Vigilance Santé Inc. This content is for information purposes only and does not in any manner whatsoever replace the opinion or advice of your health care professional. Always consult a health care professional before making a decision about your medication or treatment.

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