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Rapid Antigen Tests Better at Correctly Identifying COVID-19 in People with Symptoms than in People Without Symptoms

By HospiMedica International staff writers
Posted on 26 Mar 2021
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Rapid antigen tests are better at correctly identifying cases of COVID-19 in people with symptoms than in people without symptoms. Additionally, there are large differences in the accuracy of different brands of test, with very few meeting the World Health Organization (WHO) minimum acceptable performance standards.

These are the latest findings of The Cochrane Collaboration (London, UK), a global independent network of researchers, professionals, patients, carers and people interested in health that produces systematic reviews. Cochrane’s review assessed how accurate antigen tests and molecular tests are in determining infection in people with symptoms and in people without symptoms. They identified and summarized studies that measured the accuracy of any point-of-care tests used in hospitals or the community compared with the accepted standard laboratory test, RT-PCR, to detect current SARS-CoV-2 infection.

The first version of Cochrane’s review included 22 studies and was published in August 2020. The updated review now includes evidence from 64 studies. Most of the studies included in the review were from Europe and the US and assessed the accuracy of rapid antigen tests. Only three studies were exclusively in people without symptoms - two in people who were contacts of confirmed cases and one involved staff screening. Over half of the antigen test studies included samples from people being tested in the community, for example at test centers, emergency departments, or as part of contact tracing or outbreak investigations. Molecular test studies were mainly done in laboratories and not in the community where the tests were intended to be used.

The review authors found antigen tests were better at identifying COVID-19 in people with symptoms than they were in people without symptoms. In people with symptoms, on average 72% of people who had COVID-19 were correctly identified as being infected; tests performed best in the first week after symptoms began when they identified 78% of people who had COVID-19. In people without symptoms, on average, the antigen tests correctly identified 58% of those who were infected. Antigen tests correctly ruled out infection in 99.5% of uninfected people with COVID-19-like symptoms and 98.9% of uninfected people without symptoms.

The percentage of people with COVID-19 who were correctly identified varied between brands and also depended on whether manufacturers’ instructions for using the tests were followed. For people with symptoms of COVID-19, correct identification across test brands ranged from 34% (Coris Bioconcept assay), to 58% (Innova assay), and up to 88% (SD Biosensor STANDARD Q assay) of infected people. The WHO has established performance standards for tests that identify infection in people with symptoms. To meet these standards, a test must be able to correctly identify at least 80% of people with infection and correctly exclude infection in 97% of people who are not infected.

To illustrate their results, the researchers looked at the effect of two of the better performing brands of test (Abbott Panbio and SD Biosensor STANDARD Q ) in people with symptoms (75% to 88% of COVID-19 cases correctly identified) and in people who did not have symptoms (49% to 69% of COVID-19 cases correctly identified). In a population of 10,00 people with symptoms where there are 50 people with COVID-19, about 40 people would be expected to be correctly identified as having COVID-19 by rapid tests, and between 6 and 12 cases of COVID-19 would be missed. Between 5 and 9 positive test results would turn out to be false positives.

The true number of cases of COVID-19 is likely to be lower in mass testing of people without symptoms. In a population of 10,000 people with no symptoms, where 50 people really had COVID-19, between 24 and 35 people would be correctly identified as having COVID-19, and between 15 and 26 cases would be missed. The tests could be expected to return between 125 and 213 positive results, and between 90 and 189 of those positive results would be false positives.

“Our review shows that some antigen tests may be useful in healthcare settings where COVID-19 is suspected in people with symptoms. These tests do not appear to perform as well in people who don’t have symptoms of COVID-19. Confirming a positive result from a rapid test with a RT-PCR test, particularly where cases of COVID-19 are low, may help avoid unnecessary quarantine. All antigen tests will miss some people with infection, so it is important to inform people who receive a negative test result that they may still be infected,” said Dr. Jac Dinnes, Senior Researcher in Public Health, Epidemiology and Biostatistics at the University of Birmingham, an author of the review. “There is some emerging evidence that the accuracy of the test is affected by who is doing it. Future studies should look at the relationship between the experience of the person administering the test and the sensitivity of the test. Future research should also evaluate molecular tests in the settings in which they are intended to be used to clarify their performance in practice.”

Related Links:
The Cochrane Collaboration

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