Between 1 February and 23 March, 117,670 Danes were tested with both PCR and antigen tests within 48 hours. 4,069 of the pcr tests gave a positive answer, ie that the person was infected with the sars-cov-2 virus, while the figure for the antigen tests was only 2,159. This means that 1,910 people (47 percent) received a false negative answer from the antigen tests.
“You can look at antigen tests as a very wide sieve. It catches the most contagious, but not all who can potentially be infected. Therefore, we consider the antigen test as a screening tool. It is an extra tool for finding and fighting viruses “, says Tyra Grove Krause at the Swedish Serum Institute in a press release.
The Danish authorities emphasize that a negative response to antigen tests does not mean that one can fail to comply with coronary restrictions.
To do the thing even more complicated, there are also many who get a positive answer to the quick tests, even though they are not infected according to the pcr tests.
Therefore, it is very important that everyone who gets a positive result from an antigen test has their PCR tested as soon as possible so that they make sure that they are infected. It is only after the subsequent negative pcr test that we consider it a confirmed case. That is, that you are infected “, says Tyra Grove Krause.
Flemming Platz, press manager at the Swedish Serum Institute, tells DN that several different antigen tests are included in the survey, but can not answer how many.
– Our experience is that it is basically the same type of problem with different antigen tests. We only consider antigen tests as screening, which must be confirmed by PCR tests, he says.
According to the Swedish Public Health Agency there is a wide range of antigen tests from several different suppliers. Performance varies while several of the tests have not been evaluated by an independent actor to any great extent.
The reliability of antigen tests depends, among other things, on when in the course of the infection they are used. The probability that the test will be able to detect antigen increases with higher virus levels in the sample “, writes the Public Health Agency in a guidance for the use of antigen tests in covid-19.
The tests are designed to directly detect protein produced by the virus as it multiplies in infected cells.
“Antigen tests are generally less sensitive than PCRs, as direct detection means that higher virus levels are needed in the sample for antigen tests to give a positive result. This means that a negative test result does not exclude covid-19 “, the report states.
DN has contacted the Medical Products Agency and the Swedish Public Health Agency for more information.
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