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Pharmacies in Belgrade are advertising the sale of home tests for the corona virus, but how much do we know about their use and the accuracy of the results?
In one of the Belgrade pharmacies, they told the BBC in Serbian on Thursday that they had not yet received the tests and were waiting for them on Friday. They say a copy will cost around 1,300 dinars.
If the result is positive, then the person tested certainly has the corona virus, but if the result is negative, it does not necessarily mean that the person is not infected.
Epidemiologist Zoran Radovanović explains to the BBC in Serbian that it is an antigen test and that there are three reasons for a possible inaccurate result.
“The first reason is the wrong test time. If, for example, you were in contact with an infected person yesterday and they got infected, you cannot have a positive result today.
“The highest probability of detecting the presence of the virus is between the first and fifth days after the onset of symptoms,” says Radovanović.
Another reason, he says, is that people who test at home may not sample well enough.
“You have to push your nose through the back wall of the nasal part of the pharynx. That’s pretty embarrassing. People frown when a technician or doctor sticks a stick up their nose.
“So when you work at home and on your own, the question is whether you will get to the back wall,” says Radovanović.
Watch the video: How to wear a mask correctly
It confirms the words of the director of Pharmacy of Belgrade, Jasminka Bjeletić, that medical knowledge is needed to perform the exam.
Bjeletić told RTS that it was recommended that a person with health education use a home test for the corona virus, to avoid potential misuse.
The third reason for a false negative test, Radovanovic explains, is that many more viruses must be present for the test to be positive, compared to PCR.
“PCR detects trough concentrations – you take and multiply what it finds a million times. This is another technique, so the virus concentration must be higher for the test to be accurate.
“If there is a relatively small amount of virus on the back wall of the nasal part of the pharynx, the test will be negative,” explains Radovanović.
It says that if the sample is well taken and if the result is positive, the patient is certainly infected.
If, on the other hand, the test is negative, it may mean that there was not enough virus, because the detection threshold is higher.
“That’s why PCR is the gold standard, and it can be used under those conditions. I’m positive, that’s how it is.” I’m negative, it doesn’t have to mean, I better do PCR too, “says Radovanović.
How is the test done?
The director of the Belgrade Pharmacy explained to RTS that the test is very easy to use using samples from the nose.
“With a sterile stick, it is necessary to go deep to the root of the nose, as deep as possible, there should be no mistake not to go beyond the required level and gently remove the content of the nose, with gentle movements.”
When the contents are extracted, you add, the wand is dipped in the already prepared chemical and then pressed five times so that the contents and the antigens present inside are finally squeezed into the bottle.
After that, you need to wait up to 30 minutes for the detection to take place, he said. If the test is positive, two lines will appear.
Watch the video: How to recognize if the corona virus, cold or flu?
Difference between PCR and antigen test
Diagnostic tests, also known as PCR tests, show whether someone currently has the virus.
These tests look for signs of the genetic material of the virus.
A rapid antigen test involves a throat swab and determines the presence of the virus in the upper respiratory tract and can be taken between the fifth and seventh day from the onset of symptoms.
There are also tests to detect the presence of antibodies, that is, serological tests that are carried out from the blood.
Specific antibodies indicate the current presence of an infection or if someone has already been infected.
IgM antibodies indicate the current infection and IgG the chronic one, that is, someone has already had an infection.
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