Hey guys. Previously I talked about routine section where urine is processed for different kinds of tests. For now, I want to talk about how stool is processed to test for ova or cyst. The tests are done to identify intestinal parasites and their eggs which are known as ova or cysts in patients. The patients may or may not experience any symptoms of gastrointestinal infection. One common symptom may be diarrhea. Another symptom is blood in stool. When we are able to identify the particular parasite in the patient, we may know the cause of the gastrointestinal infection and thus we can provide the appropriate medication to treat it.
The principle of the test involves the saline wet mount. It is the recommended test to detect helminth eggs and larvae. It is also good for motile protozoan cysts which appear to be refractile. Refractile means that granules in the cells that refracts light. When cysts are detected in the saline wet mount, they are observed in Lugol iodine stained preparation. This stain will reveal the nuclear structure of the cells. The nuclei stain will be stained brown and thus can be counted easily. A kit called Para-pak spin con is a commercial kit that is used to detect the faecal parasite concentration of eggs, larvae and protozoa. Saline wet mount technique involves placing the sediment of the specimen on a glass slide. It is mixed with saline and a cover slip is place over it. A drop or two of Lugol iodine is placed on the sediment. Then, the slide is directly examined under the microscope. This technique also provides information on the content of the stool such as the presence of leukocytes.
The procedure to obtain the sediment of the specimen (stool) is by emulsifying 0.5g of stool with 10ml of saline in a plastic tube. 4 drops of CON-trate Reagent A are added to enhance the breakdown of faecal aggregates and mucus, causing the parasites to be exposed. The contents are mixed thoroughly. The mixture is then filtered using the Para-pak filter into the centrifuge tubes provided. The filtered mixture is then centrifuged at 2000rpm for 10min.
10min later, the supernatant is discarded and the sediment is resuspended. This is where the wet mount saline is performed on the sediment.
The limitations of this procedure are such as false-negatives occurring due to low number of parasites in the stool specimen. The parasites may undergo intermittent shedding which contributes to the low number. Inappropriate transport or storage may also contribute to false-negatives. False positives may occur when one of the numerous structures in the stool is mistaken for a parasite. There is no reference range for this test. The presence of normal bacteria in stool is considered normal.
Siti Nurfatin
0605853a
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14 comments:
Hi Siti Nurfatin,
Your post is rather interesting...!
1) What are some examples of normal bacteria found in the stool (besides E.coli)?
2)Can the stain differentiate different types of parasites which leads to identification purpose? How?
3)Why is the centrifuge speed set at rpm or not rcf? Difference between rpm and rcf?
4)Why is there no reference range?If there is no reference range for this test, how do you know whether the patient is diagnosed with gastrointestinal infection? Are the parasites countable? Since you have mentioned they exist in low numbers.
5)If the downsides of this test are false-negative or false positive results, are there other alternative tests to detecting parasites?
Thankz!
Han Yang
TG01
Psst..
Is there other types of stain other than Lugol iodine to observe cysts when they are detected in the saline wet mount?
Andika Putra
TG01
Hi
When u observed for cyst under the microscope, how do u know if there is presence of cyst? As in how do they look like in saline wet mount?
And are there alot of different type of cyst? If so, then do u have to report all the types that u see under the microscope after the staining?
Thanks
Zhenling
TG02
Hi
1)Have you ever come by a time when you can't identify the parasite in the stool?
2)Is there any different between Lugol iodine and the normal iodine that we use?
Justina
TG01
hello! for those cysts and eggs that can be found in stools? what are the diseases for them?thx
yuxuan
hey han yang, an example that i know of is pseudomonas. as the stain will stain the nucleus of the parasites, we can see their morphology. from there we can identify the type of parasite. there are also reference books for us to identify the parasite. for my lab, they use rpm. i have not heard of rcf though. feel free to elighten me? i would like to know. there is no reference range as when we look under the microscope, as long as there is one parasite, we can identify the parasite. then the respective diagnosis is carried out. yes the parasite is countable even as they exist in low numbers.thus this is the limitation of the test as we tend to miscount the parasites that are of low numbers. another test such as Permanent Stained Smear is used to recover and identify intestinal protozoan cysts. hope this helps!
hey andika, hmm i don't think there is any other types of stain used to detect cysts under the saline wet mount. in the lab, we use only lugol iodine as the stain.
hey zhen ling, cysts are generally cicular shaped when looked under the microscope. we have reference books to identify the types of cysts. you may take a look at thus website http://www1.indstate.edu/thcme/micro/parasites/intestpro.htm
this website gives you a better illustration of the different types of cysts present in the intestines.
yes, we have to report the types of cysts that we see. hope this helps!
hey justina, so far i have not encounter such situation where we cant identify the parasite. the difference between lugol's iodine and normal iodine is their composition. lugol's iodine is a mixture of iodine and potassium iodide. whereas the normal iodine in is predominantly iodide. hope this helps!
hey yuxuan, an example of a disease is known as Cyclospora cayetanensis. this disease is caused by a protozoan of cyclospora genus. this disease causes severe diarrhea. another type of parasite is entamoeba histolytica. this parasites destroys tissues and eventually this causes amoebic liver abscess. hope this helps!
Hello Siti,
Your post sure reminds me of some of the horror i'd experienced when i was handling the same type of samples some weeks back. Doubt i'd ever go back to that section voluntarily. Hahs.
Anyways. You mentioned that "CON-trate Reagent A (is) added to enhance the breakdown of faecal aggregates and mucus, causing the parasites to be exposed". Do you happen to know how this reagent functions? As in perhaps that it cellulose specifically only and not proteins(such as that found in the taget parasites)? Is there a limitation to its usage(for example, if the incubation time is too long, the target parasites would be broken down by the reagent too)?
Big thanks!
Alexander Soo TG02
0608122H
helo fatin =)
i wana ask u,
does the patient have to go for test to check if there is blood in their stool before they proceed to this test?
thank you
raihana~
hey alex. sorry for the really late reply. have been busy with project.
anyway, im not really sure of the reagent functions. but as far as i know it is targeted at cellulose breakdown. and there is no limitation of the incubation time.
hey rai. really sorry for this late reply. again have been busy with projects and stuff. btw to answer ur question, there is a test for occult blood detection which is done together with the test for detection of cysts and parasites. they are usually done together. hope this helps!
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