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Rapid Antigen Tests Better at Identifying Symptomatic COVID-19 Cases, Finds Study

By LabMedica International staff writers
Posted on 03 May 2021
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A review by an independent global network has shown that rapid antigen tests are better at correctly identifying cases of COVID-19 in people with symptoms than in people without symptoms.

The updated systematic review by Cochrane, a global independent network, along with leading experts at the University of Birmingham (Birmingham, UK), assessed rapid tests for the detection of SARS-CoV-2 infection (COVID-19). The review showed 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.

Tests have been developed for diagnosing COVID-19 that can provide results ‘while you wait’. Two types of rapid ‘point of care’ tests are available, both of which use nose or throat samples. Antigen tests identify proteins on the virus and come in disposable plastic cassettes similar to pregnancy tests, with results available within 30 minutes. Molecular tests detect the virus’s genetic material, using desktop analyzers or small handheld devices with results typically available in 30 minutes to two hours. The Cochrane researchers wanted to know how accurate these 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 this 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.

“Our review shows that some antigen tests may be useful in healthcare settings where COVID-19 is suspected in people with symptoms,” said Dr. Jac Dinnes, Senior Researcher in Public Health, Epidemiology and Biostatistics at the University of Birmingham. “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. There is some emerging evidence that the accuracy of the test is affected by who is doing it,” added Dr. Dinnes. “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.”

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