At my workplace, I had the opportunity to use an Influenza A & B test kit to detect the presence of the virus which might be present in nasal swabs. We use a test kit to detect the presence of these two types of influenza. It should be noted that this is a qualitative and not quantitative test. If the patient shows a positive result, we would send out the test for PCR testing.
Above: The patient's nasal swab, the test kit and the extraction reagent solution vial.
Principles of test:
The test uses the principles of an immunochromatographic assay. As you can see from the picture above, the test kit has two sides to it: Testing for Influenza A, and testing for Influenza B. The picture actually shows a test kit that had already been done, which shows a negative for both A & B. The lines seen are the control lines.
If there is a positive result, another test line would appear nearer to the middle of the control line. The test area contains monoclonal anti-human influenza virus. If there is a presence of the virus in the specimen, the virus would bind to the antibody and react to form a purple-red line.
Methods of test:
A sterile swab should be inserted into the nasal cavity and rubbed on the mucosal surface for several times to collect mucous epidermis. The swab should be at a horizontal angle.
The swab is then dipped inside the extraction reagent solution vial, which contains buffer salt and detergent with 0.09% sodium azide.
The tip of the solution vial should be squeezed to contact with the swab and the swab should be rotated clockwise and anti-clockwise 5 times so that the virus (if any) would be transferred into the extraction reagent solution.
The swab is removed and the vial is gently shaken to mix the specimen.
The vial has a dropper on top. 4 drops of the solution is added to the specimen area and incubated at room temperature for 10 minutes.
We would have to write the results in a logbook for future reference. If the test shows negative for the influenzae, the swab as well as the test kit and the vial are disposed. If it's a positive we would have to put all 3 items in a ziplock bag and we would place it aside.
Hakim
0703555C
6 comments:
Hey Hakim,
Is there any limitations to the test? Is it for primary identification of the virus in persons that have yet to develop the respective Ab? Or it can be used for all patients? (Wouldn't it be easier to just test for the Ab haha)
Yvonee
0703189A
hello hakim,
what if the purple line produced is very fade, do you report it as equivocal ? or positive ?
also is it possible for the test to have false positive due to cross-reactivity from other viruses such as mumps or para-influenza ?
thanks for sharing ! (:
kenneth
TG02
Hey Yvonee!
Yes, the test can be done for patients who have or have not developed the antibodies for the virus.
Well, if you test for the antibodies, it would show a false negative for patients who have the virus but have not yet or cannot produce antibodies to the virus.
Hey Kenneth!
If we can still see the purple line, we would consider it as positive. Just as I mentioned, we would then have to confirm the type of influenza by PCR.
The test kit has shown that there wasn't any cross-reactivity in many bacteria (e.g. E. coli, K. pneumoniae, S. pneumoniae) and viruses (e.g. mumps, parainfluenza, rhinovirus).
Hope I have answered your questions!!
8 more weeks people!!!
Hakim
0703555C
hi hakim,
may i noe what is the purpose of extraction reagent solution? why must the swab be at horizontal angle and how will it affect the results? thanks!
zi shuang
Hey Hakim,
For this test, you mention that the test is done with nasal swab?
Will the nature of the swabs affect the results? E.g. Do you accept other kinds of specimen (Throat swabs and so on). What about other tips of the swab (Dacron or rayon swab).
Cheers,
Tiong Han
Tg01
0703762E
Hey Zi Shuang!
The extraction reagent solution is used so that the virus can be diluted into the solution. The test kit needs the solution containing the virus.
When you take the sample from a patient and the swab is not horizontal, the swab will only touch the area that is more closer to the nostril. If you put the swab horizontally and the patient tilts their head back, you can insert the swab deeper, because the virus might be present there and not nearer to the nostrils.
Hey Tiong Han!
I don't really understand about the 'nature' of the swabs. However, I can tell you that the swab has to be dipped in saline first.
Other than swabs, you can do the testing using nasal aspirate. However, nasal aspirate decreases the sensitivity of the test because you have to further dilute it with saline.
Hakim
0703555C
Post a Comment