How do you do a swab for COVID-19?
The test to detect the presence of SARS-COV2 virus infection is performed by taking a sample of secretions from the nose or throat with a swab. The greater the amount of material taken, the greater the probability of detecting the presence of the virus.

 

What is the difference between antigenic or molecular testing for SARS-COV2?

There are no differences regarding the method of taking the sample. What changes is how this is examined. In the antigen test (also called rapid test) we look for the domains of some surface proteins of the virus while in the molecular test we look for specific genomic sequences of the virus itself.

 

What are the Pros and Cons of Antigen Testing?

The main advantages of antigen testing are the speed of execution and low costs. Moreover, being a slightly less specific test, it could also more easily identify any variants of the virus.

The cons are the fact that it is a less sensitive test and therefore may not detect infections at onset, when the viral load is low, or asymptomatic subjects, especially in communities where the virus is scarce.

For this reason it is advisable to wait a few days after a possible infection before carrying out the antigenic swab and, for the same reason, in the presence of a strong suspicion of infection, it is advised to repeat the antigen test after 48 hours, if it is negative.

It is also a less specific test and can provide false positive results. . For this reason, in the absence of symptoms and with little possibility of infection, it is advisable to repeat the test and possibly carry out also a confirmatory molecular swab.

 

What are the Pros and Cons of molecular testing?

The pros of molecular testing are first of all of high specificity and sensitivity. It can detect even small amounts of virus and rarely returns false positive results.

The cons are that reporting times and test costs are higher. In addition, the test can continue to be positive even after weeks even if the virus is no longer replicating and therefore lose its clinical significance.

Finally,E if the virus undergoes a mutation and a variant comes out, the molecular test could be falsely negative.

 

Which swab to do?

The attending physician will suggest the most suitable type of test for the individual patient, following the specific ministerial regulations.

 


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Bibliography

Drain PK – Rapid Diagnostic Testing for SARS-CoV-2 – N Engl J Med. 2022 Jan 7 Online ahead of print


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