Mike: Hello, I'm Mike Clarke, podcast editor for the Cochrane Library. Several of the Cochrane reviews in our collection for COVID-19 relate to diagnosis and the second update for one of these, on the use of rapid point-of-care antigen tests was published in July 2022. Here's lead author Jacqueline Dinnes from the University of Birmingham in the UK to tell us what they found.

Jac: Tests for diagnosing COVID-19 are an important tool to help reduce the spread of infection. Tests are not perfect for detecting whether or not someone has an infection and so it's important to estimate how often a test will give an incorrect result. Whether this is a false positive or a false negative, knowing how often it might occur allows us to weigh up the possible benefits and harms from using that test.
Our second update of the review of rapid point-of-care antigen tests, or lateral flow tests, looks at the evidence up to March 2021. Like PCR, rapid antigen tests use samples taken from the nose or throat, but they can be done outside of a specialist laboratory and provide results much more quickly than the PCR test.
In this update, we included 155 studies, evaluating 49 different rapid antigen tests. These studies included samples from just over 100,000 people, including almost 17,000 who had COVID-19 infection confirmed by a positive PCR test.
With each update of this review, we have seen incremental improvements in study quality and an increase in the number of studies that included people with no signs or symptoms of COVID-19. In this update, the  studies mainly included people with symptoms of COVID-19 who presented for testing at a COVID-19 test centre or other healthcare setting, but we could not always be sure how long study participants had experienced symptoms for, or even whether or not they had symptoms. In the studies, the tests were not always done in the way that the test manufacturers recommend or were carried out in laboratories by specialist personnel, which means that different results might be seen when the tests are used in routine practice.
Turning to our findings, in people with COVID-19 confirmed by PCR, lateral flow tests correctly identified the infection in an average of 73% of people with symptoms, compared to 55% of people without symptoms. For people with symptoms, tests correctly identified more people with infection when the test was used within a week of the symptoms appearing. This is likely to be because people have the most virus in their system in the first days after they are infected. For people without symptoms, tests correctly identified more people with infection when the tests were only available to people who had been in contact with someone with confirmed COVID-19 infection compared to when tests were more widely available to anyone who wanted a test. The presence or absence of symptoms and likelihood of recent exposure to a confirmed case are likely to have led to much of the variation in test accuracy that we observed when tests were used in different settings, such as COVID-19 test centres, other healthcare settings, schools or universities or for screening purposes.
In people who did not have COVID-19 or who had negative results on PCR tests, rapid antigen tests correctly ruled out infection in 99.1% of people with symptoms and 99.5% of people without symptoms.
We saw a lot of variation in the sensitivity of different brands of tests and our overall results combine findings from different studies that evaluated the same tests. When we limited the analyses to studies that followed the manufacturer's instructions, only seven tests met international standards of 'acceptable' accuracy when used in people with symptoms of COVID-19. We did not find any tests that met this standard when evaluated in people without symptoms.
In summary, rapid antigen tests continue to be an attractive and potentially important tool for managing the spread of COVID-19. The tests are considerably less able to detect infection when people do not have symptoms of COVID-19 but do perform slightly better in people who are more likely to be contacts of confirmed cases. Thus far, we have not been able to consider any effect on accuracy of vaccination status or SARS-CoV-2 variant but we hope to consider any relevant evidence in a future update of this review.

Mike: If you would like to read the current version of the review and to watch for its third update, it's available free on Cochrane Library dot com. If you go to the website, and type in a search for 'antigen tests for COVID-19', you'll find it.