Few COVID-19 tests up to standard, especially for those without symptoms

MedTech News: Rapid COVID-19 tests, which can give results in minutes or hours rather than days, would miss almost half of COVID-19 cases in those without symptoms, according to a new Cochrane review. 

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 analysers or small handheld devices with results typically available in 30 minutes to 2 hours.

The Cochrane systemic review shows that rapid antigen tests are better at correctly identifying cases of COVID-19 in people with symptoms than in people without symptoms. 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.

In people with symptoms, on average 72% of people who had COVID-19 were correctly identified as being infected by the antigen tests; 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 have 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).

Dr Jac Dinnes, Senior Researcher in Public Health, Epidemiology and Biostatistics at the University of Birmingham, an author of the review said “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 standard laboratory 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. 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.”

Author, Jon Deeks, Professor of Biostatistics at the University of Birmingham added “It is good to have found evidence that some test brands do meet the minimum ‘acceptable’ performance standards set by WHO for testing people with symptoms. However, they represent only a very small proportion of the commercially available tests. The situation is different for testing people without symptoms, particularly for the use of repeated rapid antigen tests to screen for SARS-CoV-2 infection in school pupils and staff, and hospital and care home workers. We didn’t find any data or studies evaluating the accuracy of these tests when used in repeated screening of people with no known exposure to SARS-CoV-2. These testing policies have been implemented without any supporting real-world evidence.”

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