Sunday, September 14, 2008

Week 12

This month I will be introducing to you guys about a new method that I learnt in the microbiology department how to detect the presence of occult blood in stools specimens.

My company uses a kit called Hema-Screen. It is a guaiac slide test for the qualitative detection of fecal occult blood. It is a useful aid in diagnosis of a number of gastrointestinal disorders.

The detection of occult blood is critical to many gastrointestinal diseases. The presence of occult blood in fecal material may indicate gastrointestinal pathology such as hemorrhoids, diverticulitis, fissures, colitis or colorectal cancer. Hence Hema-Screen is a simple, aesthetic, inexpensive test designed for the use in collection and preparation of stool specimens. It overcomes the instability of guaiac solution and the hypersensitivity of benezidine and ortho-tolidine.

The principle of the test is as follows. Hema-screen is composed of guaiac impregnated paper enclosed in a cardboard frame, which permits sample application to one side, and development and interpretation on the reverse side. The process involves placing 2 specimens onto the guaiac paper.

Hema screen, like all guaiac paper test for occult blood, is based on the oxidation of phenolic compounds present in the guaiac to quinines resulting in production of the blue color. Because of its similarity to the prosthetic group of peroxidase, the hematin portion of the hemoglobin molecule can function in a pseudoenzymatic manner, catalyzing the oxidation of guaiac. So when a fecal specimen containing occult blood is applied on the test paper, contact is made between hemoglobin and the guaiac. A pseudoperoxidase reaction will occur upon addition of the developer solution, with a blue chromagen formed proportionally to thee concentration of hemoglobins. The color reaction will occur after 30 seconds.

If a positive result is obtained with the test, a follow-up with additional diagnostic tests, as soon as possible, is essential. As with any occult blood test, results with Hema-Screen cannot be consider conclusive evidence of the presence or absence of gastrointestinal bleeding or pathology. The test is not intended as a replacement for other diagnostic procedures such as proctosigmoidoscopy examination, barium enema, and X-ray studies.

Ivan Ng


SIP said...

May i know what is guaiac? And is it this the only test for occult blood in stool? or are there more effective methods available?

Ying Chee

tg01 group 2 said...

Hi Ivan,

Your post is very reader-friendly...! :)

I got some questions to ask...

1)Can you kindly define and explain on proctosigmoidoscopy examination, barium enema, pseudoenzymatic manner and aesthetic? I don't quite understand the above terms...

2)What is the pathogenesis of hemorrhoids, diverticulitis, fissures and colitis?

3)What are benezidine and ortho-tolidine?

4)What are the downsides to this test?

5)What are the appropriate PPE to wear when dealing with this test and what are the possible hazards and precautions to take note pertaining to this test?


Han Yang

group1 said...

oh man, han yang have already asked all the questions that i want to ask.

anyway, just some question, how are the results shown? positive or negative? or does it shows the degree of severity?

how does a negative result appear to be?

YuMei, TG01

De Incredibles said...
This comment has been removed by the author.
De Incredibles said...

Ya, all questions had been asked..not much left to here goes..

Is there anything the patients need to take note before taking the specimens from them?eg. dietary restriction?

when u mention "It overcomes ......the hypersensitivity of benezidine and ortho-tolidine", does it means that other than guaiac, benezidine & ortho-tolidine can also be used juz that they are too sensitive (thus not used)?

Lim Xin Ni

De Incredibles said...

Hi Ivan,

Q. Is there a common appearance of the feces among the samples with positive occult blood test?

Q. Also, hows does the patient knows he/ she has occult blood loss? signs and symptoms?

Q. I know the traces of blood are very little and cannot usually be seen by eye, but if there's really severe bleeding, can we see the blood and will the blood in the feces appear as reddish or black?

thanks alot =)

Jean Leong

tg01 group 2 said...

Reply to Ying Chee

Guaiac is a chemical reagent in the kit produced by Guaiacum tree. Since this is the only method or kit used by my company to detect occult blood, and my company recently acheived ISO cert, hence i suppose it should be the most effective method. Furthermore has a company who directs at profits, this is the most cheapest, efficient and economical method.

From Ivan

tg01 group 2 said...

Reply to YuMei

Just look for any green or blue color at the reverse side of the kit/card. If a green/blue color appear, it means the presence of hemoglobin, thus blood maybe present. Further confirmatory test must be done to confirm the presence of blood. Negative result is reported when there is no color change after the developer solution is added.

From Ivan

tg01 group 2 said...

There is no differences between feces with or without occult blood. Signs and symptoms of the diseases i stated do not occur readily in the early stage. It is only when at the later stage where the diseases states gets worsen and he or she go for a medical check up. This test is usually done during routine physical examinations, hospital testing and mass screening for colorectal cancer.
Reply to Jean Leong

Regarding the last question, we do not see the color of the feces to determine whether occult blood is present. Color is independent to the presence of occult blood. As a professional point of view, regardless of the color, we will do the test to confirm the presence of occult blood.

From Ivan

Ms_chew said...

What is the confirmatory test for occult blood in stool?

tg01 group 2 said...

Reply to Ms Chew

Proctosigmoidoscopy examination, barium enema, and X-ray studies are the confirmatory test for occult blood in stool.

From Ivan

tg01 group 2 said...

Reply to Lim Xin Ni

the patient must avoid red or rare meet in their diet. Raw fruits and vegetables such as turnip, cauliflower, red radishes, Broccoli, Cantaloupe, Horseradish and Parsnip must also be avoided, because these food contains high peroxidase activity which can cause false positive results.

The hypersensitivity part refers that to the handler or the one doing the test to detect occult blood.Benezidine and ortho-tolidine can cause hypersensitivity reaction to the handler or tester.

From Ivan

tg01 group 2 said...

Reply to Han Yang

Proctosigmoidoscopy examination, barium enema are just some of the confirmatory test to diagnose the patients of having occult blood and gastrointestinal diseases.
pseudoenzymatic means mimic the enzymatic reaction which involves in the test.

Benezidine and ortho-tolidine are alternative ways in detecting occult blood in stools.

The down side of this test is that diet of a person strongly affects the results of the test. Strict diet or restriction diet must be performed on the patients.

there are no special PPE in dealing the tests. just gloves, lab coat is enough. note that all test results must be read and analyzed after 30 seconds and within a minute. If not the results whill be unreliable.

From Ivan