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How accurate are corona rapid tests?

Rapid tests carried out by trained staff should be the key to safe school openings and more visitors to retirement and nursing homes. They should identify people infected with the coronavirus at an early stage, before they can infect others.

But this only works if the tests are actually very informative. That is why Cochrane, a global, independent network of scientists, evaluated 64 studies from the USA and Europe for rapid tests. In these studies, the results of the rapid tests were compared with PCR tests.

When evaluating the 64 studies, the experts came to the following results:

Many rapid tests do not meet the minimum requirements of the WHO

There are significant differences in accuracy between the rapid tests available on the market. Only a few meet the minimum requirements set by the World Health Organization (WHO): According to this, the tests should identify at least 80% of infected people and correctly rule out the infection in at least 97% of those who are not infected.

On average, however, the antigen tests identified only 72% of the patients infected with SARS-Cov-2 who had the corresponding symptoms. These tests performed best in the first week after symptoms began, when they identified 78% of people with COVID-19.

In the people infected with SARS-Cov-2 without symptoms, only 58% were correctly identified.

One of the better tests that met the WHO quality criteria in the studies was the SD Biosensor Standard Q. The scientists carried out the following model calculation for this test:

Model calculation when testing symptomatic patients

If 1000 people with symptoms typical for Covid were tested with the SD Biosensor Standard Q, 50 of whom were actually sick with Covid-19, the following results would on average be obtained:

  • There would be 53 positive test results, of which 9 people (17%) would not be infected at all, i.e. they would be false positive results.
  • There would be 947 negative test results, of which 6 people (0.6%) were sick with Covid-19 without the test having discovered them.

Model calculation when testing symptom-free people

If 10,000 people were tested without symptoms of the disease, of which 50 people were still infected with SARS-CoV-2, the following results would on average be obtained:

  • There would be 125 positive test results, of which 90 people (72%) would not be infected at all, i.e. they would be false positive results.
  • There would be 9,875 negative test results, of which 15 people (0.2%) were sick with Covid-19 without the test discovering them.

Accurate execution is an important factor

The analysis gave you some new evidence that the accuracy of the test is affected by who is doing it. Future studies should therefore investigate the relationship between the experience of the person taking the test and the sensitivity of the test.

Mixed conclusions from the researchers

First author Jacqueline Dinnes, Senior Researcher in Public Health, Epidemiology and Biostatistics at the University of Birmingham, comments, "Our review shows that some antigen tests can be useful when people with symptoms are suspected of having COVID-19." Rapid tests are therefore accurate enough to temporarily replace a PCR test in people with Covid symptoms, especially when quick decisions have to be made when caring for the patient.

However, these rapid tests don't seem to work as well in people who don't have symptoms of COVID-19.

A positive result from a rapid test should always be checked with a PCR test. This can help avoid unnecessary quarantine measures - especially when there is a low frequency of COVID-19 cases.

Important: All antigen tests miss some people with an infection. It is therefore important to make it clear to people who receive a negative test result that they can still be infected.

No evidence yet of the benefit of the rapid tests in screening

Co-author Jon Deeks, Professor of Biostatistics at the University of Birmingham, added: “It is good that we found evidence that some test brands meet the WHO minimum standards of performance for screening people with symptoms. However, these only make up a very small fraction of the tests available commercially. "

The situation is different when testing people without symptoms, especially when using repeated rapid antigen tests to screen for SARS-CoV-2 infections in schoolchildren and staff in schools as well as in hospital and nursing home staff. Deeks continued, “We have not found any data or studies that assess the accuracy of these tests when used in repeated screening of people with no known exposure to SARS-CoV-2. Such test strategies have so far not been able to rely on real-world evidence from practice. "

Listening instead of reading - the podcast "Klartext Corona"