In late August the FDA (United States Food and Drug Administration) approved the use of rapid antigen tests as an emergency measure to fight the coronavirus.
The rapid antigen test is the size of a credit card and “ instead of identifying genes, we look for proteins, usually protein S which is usually the place where the virus binds to the host cell . Other times a nucleocapsid protein (N) is used, which is the envelope that protects the genetic material of the virus ”, explains Guillermo Quindós Andrés, professor of Medical Microbiology at the University of the Basque Country.
As in everything, this test has its pros and cons. If we compare it with the test that is currently used the most in Spain to detect the coronavirus, the PCR, the antigen detection test is much cheaper, € 5 compared to the € 100 that each PCR costs . In addition, it gives results in much less time . If with PCR it takes at least 24 hours to know if a person is positive or negative for the coronavirus, with the antigen test the unknown is solved in less than 30 minutes and without the need for the sample to pass through the laboratory.
As for the disadvantage of the antigen test compared to PCR, it is not as sensitive as this, since PCR is capable of detecting minute amounts of the SARS-CoV-2 virus, something that the antigen test does not achieve . In this sense, some experts see danger that people who are infected are not detected and can lead to new outbreaks. Proponents of the antigen test, however, consider the lower sensitivity to be an advantage because some people who receive positive PCR test results are infected but can no longer transmit the virus to others. Currently it is believed that the period in which the contagion occurs does not go beyond 7 or 10 days after starting to have symptoms.
According to an article published in the journal Nature , “while a typical PCR test can detect a single RNA molecule in a microliter of solution, antigen tests require a sample containing thousands – probably tens of thousands – of virus particles. per microliter to produce a positive result. Therefore, if a person has low amounts of virus in his body, the test can give a false negative result ”. In this regard, what is known so far is that a person with high levels of the virus is more likely to infect others than someone with very low levels .
Currently there are several companies that are working on the development of rapid antigen tests that are a simple strip of paper (now the sample is taken from the nasopharyngeal area and is done by a toilet). The person places saliva in a tube, inserts the strip and knows in a matter of minutes if they are infected with coronavirus or not. The idea is that the test can be bought at the pharmacy and one can do it at home.
Something important in what the experts emphasize is that, if it were the case, antigen tests should not replace the preventive measures: safe distance between people, use of a mask and hand hygiene .
