What is Faecal Occult Blood test?

The faecal occult blood test is performed to check the presence of traces of blood in stools that can’t easily be seen with a naked eye - the term occult means hidden. This test is usually done as to screen for colorectal cancer. However, it is also ordered when bleeding is suspected in either upper or lower parts of the gastrointestinal tract. 

Two different methods are available for this test. These include:

  • Guaiac-based test: It identifies the heme part of haemoglobin the stool sample, which can be from any source including foods such as red meat. Thus, it is less specific and can give false-positive results if red meat is consumed. This test is rarely performed because it may give false-positive results.
  • Immunochemical faecal occult blood test: It is a highly specific test that only detects the globulin part of blood in the stool sample. This is only done to screen for colorectal cancer. 
  1. Why is Faecal Occult Blood test performed?
  2. How do you prepare for Faecal Occult Blood test?
  3. How is a Faecal Occult Blood test performed?
  4. What do Faecal Occult Blood test results mean?

A faecal occult blood test is mainly done to screen for colon cancer in people over the age of 50 or to those who have a family history of this cancer.

It is also used to diagnose gastrointestinal conditions that may cause tissue damage and leakage of blood. 

Blood in stool may occur due to the following conditions:

  • Gastric ulcers 
  • Inflammation of the lower rectum
  • Rectal tumour
  • Inflammatory bowel disease (IBD)
  • An adverse effect of medications such as NSAIDs
  • Vigorous exercising 

A faecal occult blood test may also be ordered if your doctor suspects that you have anaemia and show the following symptoms:

  • Fatigue
  • Weight loss
  • Lightheadedness
  • Abdominal pain
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Your doctor will ask you about your family history, to determine the cause of your symptoms. The purpose of the test and the need to collect the stool sample will be explained to you. 

You will be instructed not to eat any red meat for at least three days before the test. Tell your doctor if you are taking any medicine with or without prescription or any supplementation as some medicines can interfere with the results of this test. Bleeding cannot be detected in one stool sample; therefore, multiple stool samples should be collected on different days to increase the chances of obtaining accurate results.

You’ll be provided with a home kit to collect the sample. Follow all the information stated on the kit to avoid sample contamination. Several stool samples are collected at different days to get optimum results. After collection, the samples are tested in the laboratory. The procedure of collection varies for the two types of faecal occult blood test:

Immunochemical faecal occult blood test

  • For this test, you will be provided with a container to collect the stool sample. Submit the sample to the lab as soon as you collect it. 

Guaiac-based test

  • For this test, you’ll be provided with a test card with three sections for collecting stool samples on different days
  • Smear the sample with the help of the application stick provided in the kit
  • Once the sample is dry, return it to the doctor by mail or in person.
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Normal results:

  • The normal results of this test are written as negative. They mean that no blood was detected in the given stool sample.

Abnormal results:

Abnormal results are written as positive, indicating the presence of blood in the given stool sample. The following could be the possible meaning of abnormal values:

If you get abnormal results in this test, your doctor will suggest further tests such as colonoscopy to find the affected area. 

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.


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  2. International Foundation for Gastrointestinal Disorders [Internet]; U.S.A. Alarm Symptoms: A Cause for Alarm?
  3. UFHealth [internet]: University of Florida; Iron deficiency anemia
  4. Rex D, et al. Colorectal cancer screening: recommendations for physicians and patients from the U.S. Multi-Society Task Force on Colorectal Cancer. Amer J Gastroenterol. 2017;112:1016-1030. PMID: 28555630
  5. MedlinePlus Medical Encyclopedia: US National Library of Medicine; Fecal Occult Blood Test (FOBT)
  6. Wolf AMD et al. Colorectal cancer screening for average-risk adults: 2018 guideline update from the American Cancer Society. CA Cancer J Clin. 2018 Jul;68(4):250-281. PMID: 29846947
  7. Robertson DJ, et al. Recommendations on fecal immunochemical testing to screen for colorectal neoplasia: a consensus statement by the US Multi-Society Task Force on Colorectal Cancer. Amer J Gastroenterol. 2017;112:37-53. PMID: 27769517
  8. Pagana KD, Pagana TJ, Pagana TN. Mosby’s Diagnostic and Laboratory Test Reference. Stool Cancer Screening. 14th ed. Elsevier. 2019. Pp:872-874.
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