Immunological Fecal Occult BLood

Hey guys!

Actually I promised you guys to continue the part II of my urine FEME, but I realised Azeimah had already done a very good job! Haha yup so think today I will share with you guys what I'm doing for my MP instead :)

I believe many of you guys had read on quite a few posts on testing for fecal occult blood(OB) using the guaic-based stool card. This is a screening test to detect for bleeding from anywhere of the GIT, particularly for colorectal cancer.

For my MP, i'm researching on the incidence OB. But instead of using the chemical method of stool card, my lab uses a machine called OC-Sensor DIANA.

OC-Sensor DIANA


OB casette

Pic 1: The whole OB casette
Pic 2: The body of OB casette and the 'cap' of OB casette
Pic3: The tip of the 'cap' of the OB casette where we smear stool around it and cap it back to the casette body

This is an immunological method that uses the principle of latex agglutination reaction and an optical measurement method. The method is quite simple actually... the stool usually arrives in an OB casette. After that we just need to place the casette into rack and run the machine to get the results!

How it works?
If a person suffers from OB, there will be present HbAo hemoglobin in the stool.
OC-Sensor DIANA uses a latex reagent, which is prepared by sensitizing anti-human HbAo antibodies to polystyrene latex particles, to detect for the hemoglobin in stool. Upon addition of stool sample to the latex reagent, a latex agglutination will result due to the reaction of sensitized HbAo antibodies to HbAo hemoglobin in the stool sample.

Sensitized HbAo antibodies(in latex reagent) + HbAo hemoglobin(in stool) = latex agglutination

This reaction is then analyzed accordingly to the change in optical density. The higher the concentration of HbAo in the sample, the greater the change in the optical density.

Why is immunological method better?
-Unlike the stool card that indicates positivity through colour changes, OC-Sensor DIANA is able to provide an exact value of the amount of OB in the stool. If the optical density > 100 ng/mL, it indicates that the person is suffering from OB. Hence with the exact value known, we can tell whether the patient is suffering from mild or serious fecal occult bleeding.

-If using the stool card, a patient need to avoid a variety of food 24-72hrs before the test to prevent false results. This is because the hydrogen peroxide used to detect for OB can be interfered by many food. For OC-Sensor DIANA, no dietary restriction is required.

-For OC-Sensor DIANA, the sample can be kept for 21 days if refrigerated. But for stool card, if the stool is harderned, the colour change will not be obvious.

Disadvantages of immunological method....
The only disadvantage of using OC-Sensor DIANA is that the test must be performed in laboratory. For stool card, if you have the necessary materials you can simply perform the test yourself at home. So the stool card is a more conveneint method.