What are antigen tests and how do they work?
The antigen test detects the envelope proteins of the corona virus.
An antibody binds to the corona proteins, and if there is a link, a color reaction is formed, and this is the blue stripe we see in the test.
The binding of the antibody to the virus protein requires a relatively large amount of the virus protein, so the test is not sensitive.
PCR testing has the identification and replication of the genetic material of the virus (rather than the protein), so the test is much more sensitive.
What is the accuracy rate of the antigen compared to the PCR tests?
There are many data on the sensitivity of antigen tests, some describing a sensitivity of 90% relative to PCR tests, some much less.
Apparently, in everyday life antigen tests are around 80% sensitive compared to PCR tests.
Should some tests be performed to increase antigen detection ability? If so, at what intervals?
Repeated sampling is likely to detect a patient because at some point the viral load will be high enough to be detected by testing the antigen.
Therefore, even if you received a negative response to the antigen, there is value in performing another antigen test after 24 hours.
I came out negative in antigen and then positive in PCR. Why is this happening?
It makes a lot of sense that a person who just contracted and is at the onset of the disease would be positive on PCR, but negative on the antigen test.
Therefore there is no point in testing an antigen immediately after exposure, but after a certain time, say 72 hours from exposure.
In addition, a PCR test can turn out positive even if the person has recovered, because there are still remnants of the genetic material of the virus left in his body, even though it is no longer contagious.
Is it true that antigen tests have difficulty locating an asymptomatic patient?
Yes, in many cases, but certainly not in all.
An asymptomatic person does not contain large amounts of the virus, so the antigen test does not identify his sample as positive.
It is important to remember that this does not mean that the person is not contagious.
Why is it said that in order to increase the ability to identify a person as positive for the micron, one must also sample from the pharynx?
The purpose of sampling is to collect as much relevant biological material as possible.
Because the virus is in the airways, when we sample both the nose and the pharynx, we collect more samples and thus increase our chances of detecting the virus.
Dr. Sorek is the director of the Laboratory of Microbiology and Outbreaks at Assuta Ashdod Public Hospital.
Brought to print: Meital Yasur-Beit Or
Were we wrong?
Fixed!
If you found an error in the article, we'll be happy for you to share it with us