Fecal Occult Blood (FOB) Test: Introduction, Principle, Procedure, Result Interpretation, and Keynotes

Introduction of Fecal Occult Blood (FOB) Test

The faecal or Stool Occult Blood Test is the common routine test in the clinical laboratory to find out the hidden blood passing in the faeces.  Bleeding into the intestine may cause the passage of blood in the stool/faeces. When the bleeding is chronic with only a small volume of blood being passed through faces, the blood is not seen in the stool and is referred to as occult or hidden blood. The commonest causes of positive occult blood in tropical countries include parasitic infection (hookworm) and gastrointestinal disorders such as colitis, polyps, and diverticulitis.

Faecal Occult Blood (FOB) Test: Introduction, Principle, Procedure, Result Interpretation and Keynotes
Fig. Faecal Occult Blood (FOB) Test-Positive


In the ‘Faecal Occult Blood (FOB)Test’, oxygen is produced when the haemoglobin in the blood reaches contact with hydrogen peroxide (H2O2) the liberated oxygen reacts with a chromogen (aminopyrine) to yield a blue colour.

Test Requirements

Hemospot/ Faecal Occult Blood test kit uses the standard guaiac method to determine occult blood in the stool. Kit contains-

  • Test card having two test and control pads (A and B)
  • The developer solution-Dropper bottle contains the developer solution and it is ready to use.
  • Positive Control
  • Sample applicator
  • Extra need- Gloves
  • Waste discarding bin


  • Put the mixed stool sample on the test card sample pad by using an applicator.
  • Spread it and leave it for drying.
  • Now, add a developer solution.
  • Note the result within 5 minutes.
  • Do not forget to run positive control to validate the testing procedure.

Result Interpretation

Positive: Presence of Blue Colour

Negative: Absence of blue colour

Positive control: It should express blue colour which will represent validation of the test procedure.


  • Instruction to the patient-
  1. For one day before the FOB test, the patients should not eat any meat and meat production.
  2. Do not use any iron-containing drug.
  3. Do not brush his teeth vigorously.
  • Older kits were cumbersome but this Hemospot kit is very simple to handle.
  • The Hemospot kit is very convenient since no sample preparation is required and also kit is storable at room temperature for 2 years.
  • Cortez Fecal Occult Blood RapiCard Insta Test uses the technology of immunochromatographic sandwich assay and therefore its sensitivity and specificity are higher than the conventional guaiac method.
  • The faecal Occult Blood test in short is also called the FOB test.
  • In the case of a positive test, additional testing such as a colonoscopy is needed to locate the source of the bleeding.

Further Readings

  1. https://www.indiamart.com/proddetail/microxpress-hemospot-kit-22255053573.html
  2. http://www.rapidtest.com/index.php?i=Cancer-Rapid-tests&id=207&cat=22
  3. https://homehealth-uk.com/all-products/5-x-gp-professional-bowel-colon-faecal-fecal-occult-blood-fob-test-pack/

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