Fecal (Stool) Occult Blood (FOBT) Lab Test

Hemoccult, Guaiac smear test
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Clinical Definition of Fecal (Stool) Occult Blood (FOBT)

Faecal occult blood testing (FOBT) is testing that is performed on samples of stool in order to detect occult blood (blood that is not visible to the naked eye) in the otherwise normal-coloured stool. Faecal occult blood usually is a result of slow (often intermittent) bleeding from inside the upper or lower gastrointestinal tract. The slow bleed does not change the colour of the stool or result in visible bright red blood.

Therefore, the blood is found only by testing the stool for blood in the laboratory. Occult bleeding has many of the same causes as other forms of more rapid gastrointestinal bleeding, such as rectal bleeding (passage of red blood and/or blood clots rectally) and melena (black tarry stool as a result of bleeding from the upper intestines such as ulcers).

What is the Fecal Occult Blood Test?

The faecal occult blood test, or stool occult blood test is done in order to check the sample of stool for the presence of blood. Occult blood refers to blood which cannot be seen by the naked eye and may be present in normal-coloured stool. The blood in the stool is usually discharged as a result of the slow bleeding in the gastrointestinal tract and does not change the colour of the stool at all.

Therefore, it is necessary to check the stool in a lab in order to identify the presence of the blood in the stool. The process of testing for the faecal occult blood is also called the hemoccult test.

The blood may mix with the stool as a result of bleeding in the colon or the rectum of the patient. The bleeding occurs as a result of colon cancer or polyps, although it is not necessary that all polyps may bleed. The test itself only confirms the presence of blood in the stool- it does not necessarily mean that the patient has polyps or colon cancer.

When do you expect results?

24 to 36 Hours

Why Get Tested?

The FOBT is ordered to detect gastrointestinal bleeding which may be an indicator of colon cancer or as a part of a routine examination to detect or diagnose colon cancer. A secondary use of FOBT is to detect the cause of anaemia, such as blood loss from a bleeding ulcer.

In people who are older than the age of 50, colon cancer represents a real risk. The test must, therefore, be done every year in order to check for onset of cancer in the body. The patient may also be required to undergo various screening tests so that the doctor can get a real look at the colon directly.

In people with anaemia, the cause cannot be found in some cases. In such patients, the presence of blood in the stools may point to the presence of a bleeding ulcer in the gastrointestinal tract, which will be the cause of the fatigue and anaemia.

Reason to take Fecal (Stool) Occult Blood (FOBT) Test

Symptoms observed are:

• Fatigue

• Low haemoglobin and haematocrit

• Unusually dark stools

Preparations Needed for Fecal (Stool) Occult Blood (FOBT) Test

Preparatory instructions before the test *:

No special preparations required.

You should consult with the doctor, however, and he may tell you to avoid certain food items or medicines depending on your diet. Commonly, he may ask you to avoid some vegetables like broccoli and turnips, red meat, horseradish, and pain relievers like aspirin and ibuprofen.

Sample Required for Fecal Occult Blood Test?

Specimen type: Stool

Specimen collection procedure: Hands must be washed before beginning the procedure.

Pass the stool specimen directly into the clean stool container provided.

  • DO NOT pass the specimen into the toilet.
  • DO NOT urinate on the specimen or into the container.
  • DO NOT allow any water to mix with the specimen.
  • DO NOT contaminate with toilet tissue.

The specimen must be returned to the lab within 1 hour of collection.

In the stool guaiac test, you will be given a test card with space for three samples, or even three separate cards. You will be required to apply a smear of your stool from two or three consecutive days on the card, and pass it to the lab after the sample has dried.

You should take care to avoid contamination of the card in any way.

How do you understand FOBT result?

Reference Range Interpretation

Negative

If the result for the test is negative, it means that there is no presence of blood in your stool sample. Therefore, it means that the patient only has an average risk when it comes to colon cancer. Your doctor might still recommend you to carry out the test after a year if you are older than 50 years of age.

Normal

A positive result in the test means that there has been blood in the sample of your stool. Your doctor might then recommend additional tests like colonoscopy to determine the reason behind the bleeding.

Understanding results of Fecal (Stool) Occult Blood (FOBT)

Reference RangeInterpretation
NegativeNormal

‘*A Reference range is a set of values which helps the healthcare professional to interpret a medical test. It may vary with age, gender, and other factors. Reference ranges may also vary between labs, in value & units depending on instruments used and method of establishment of reference ranges’

References

  1. https://www.mayoclinic.org/tests-procedures/fecal-occult-blood-test/about/pac-20394112
  2. https://medlineplus.gov/labtests/fecaloccultbloodtestfobt.html
  3. https://labtestsonline.org/tests/fecal-occult-blood-test-and-fecal-immunochemical-test
  4. http://www.cancervic.org.au/preventing-cancer/attend-screening/bowel_cancer_screening/faecal_occult_blood_tests
  5. http://www.cancer.gov/publications/dictionaries/cancer-terms/def/guaiac-fecal-occult-blood-test
  6. https://bpac.org.nz/BT/2012/June/06_faecal_occult.aspx