how they work, reliability, price and other questions


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On September 22, the Ministry of Health approved the use of antigen tests to check if a person carries the Covid-19 or not. The Ccommunity of Madrid was the pioneer and the one that demanded, among other regions, its massive use to stop the advance of the coronavirus pandemic. At first, many experts questioned its effectiveness, although the second generation of tests have improved substantially. But … how reliable are antigen tests? How much do these tests cost and how do they work?

Antigen tests are the least invasive and fastest test

The advantages offered by antigens is their easy use, since it is only necessary to use a stick or swab and take a sample of the mucosa. Then the cotton with the sample is placed on a piece of cardboard, the size of a card, where are the reagents that will tell if the result is positive or negative, using two lines if you have the cornavirus, and one if you don’t. The time you have to wait to find out is about 15 minutes on average, much faster than PCR tests, which can take days.

Reliability and price of antigen tests

The antigen test should be done to those who do not have symptoms. The Community of Madrid acquired at the end of October more tests of this type for 22.5 million euros, where it also stated that the reliability of the antigen test was greater than 93%. However, from the Alerts and Health Emergencies Coordination Center, Fernando Simón made a call not to use this type of test in all situations, since its efficacy in symptomatic patients is “high”, but in asymptomatic patients it “loses sensitivity”, so that today the most reliable tests are still the PCR, although antigens decongest labs.

Another advantage antigens have is price. While a test it costs 4’5 euros for public administrations, PCRs usually reach € 100.

When should these tests be done?

The WHO recommends that antigen tests should be done in the days before symptoms, as well as in the first ones in which they already have, but after this time the percentage of success decreases. The agency ensures that antigen tests work well with patients who have a high load of the virus. Likewise, this entity does not recommend the use of this test for asymptomatic patients, unless there has been contact with a positive person.

For its part, the Public Health Commission of the Ministry of Health described them as a “rapid diagnostic and screening tool.” They also indicate that it is a good option to carry them out “by people with symptoms and those directed to the study of outbreaks in strategic settings and in certain settings such as health, social and educational centers.” What it does not mention is the massive screening to which other autonomous communities do refer.

On the other hand, the FDA (The US Food and Drug Administration admits that it is a virus-specific test, but not as sensitive as PCR: “This means that positive antigen test results are very accurate, but there is a higher probability false negatives, so negative results do not rule out infection.

Madrid and Catalonia want antigen tests in pharmacies

These tests have been so successful in recent weeks that the Community of Madrid and Catalonia want pharmacies to also open up the possibility of carrying them out, with the consent of the Ministry of Health. Ignacio Aguado, Vice President of the Community of Madrid, has already demanded from Minister Salvador Illa the meeting of the Covid-19 Group, in order to be able to incorporate these rapid tests: “It would be a before and after in the diagnosis of Covid.” In fact, Madrid’s plan is that the population can test for free before Christmas.

On the other hand, the Catalan Minister of Health, Alba Vergués, informed about the plan that the region has to carry out antigen tests in pharmacies. “Any tool that we can make available to control the pandemic will be good.” The problem that Health sees is that those people who have symptoms do not go to the pharmacies: «We cannot think that a person with symptoms goes to a pharmacy and gets tested. This has the risk that staff can become infected and lose their workers. We have to be aware of the associated risks, ”Fernando Simón commented at a press conference.

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