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The retail chain Boots have announced the launch of an in-store COVID-19 testing service, targeted at those without symptoms.
Dr Alexander Edwards, Associate Professor in Biomedical Technology, Reading School of Pharmacy, University of Reading, said:
“It is good to see new testing services becoming available. This LumiraDx product appears to be a swab antigen test, that detects viral antigen (i.e. components of the virus particle) using what is known as lateral flow testing, which is the same technology as pregnancy tester. This contrasts with RT-PCR swab tests that detect viral RNA, using very different methods.
“There will be differences in accuracy for this test vs other tests, such as the most commonly used RT-PCR test. However it’s important to put this difference in context – each and every test will have its own strengths and weaknesses, and none are perfect. For example, swab RT-PCR test products vary in performance – for example the US FDA compared many different products side-by-side and found very significant differences. All were able to detect virus in those patients who had high levels of virus, but quite a few people can only be picked up by the more sensitive products, and other products give false negative (e.g. early or late in the infection, when we’d expect the levels of virus to be lower than during the most intense infection phase). Furthermore, if the swab is not taken correctly, it could miss the virus altogether – no test will detect virus if there is none on the swab.
“There have been comparisons of “antigen” vs “nucleic acid” swab tests, in some case showing antigen tests are less sensitive and therefore pick up fewer infected people. However, if you don’t have access to nucleic acid test, these are still extremely useful – when used as part of a wider public health program that can take into account the test accuracy.
“The biggest concern about swab tests is false negatives, which are possible because you can be exposed to virus, become infected, but it can take several days before there is enough virus in your swab to be detected by any test. Typically, it is expected that most swab ‘am I infected now?’ tests can pick up around 80% of infected people (RT-PCR or antigen), but this still means around 1:5 infected people could be missed in any of the tests. Furthermore, the real-world accuracy may be different from controlled trials. Testing is useful if it prevents people transmitting the virus, but it’s still complicated to use testing to reduce spread, and public health systems need a full understanding of test performance to achieve public benefit.”
Dr Julian Tang, Honorary Associate Professor in Respiratory Sciences and Clinical Virologist, University of Leicester, said:
“The press release is slightly confusing in places. The test they cite, LumiraDx, have details on their website here – freely accessible to all: https://www.lumiradx.com/assets/pdfs/covid-19-antigen-test/sars-cov-2-ag-test-spec-sheet-us.pdf and https://www.lumiradx.com/assets/images/new/pdf/sars-cov-2-ag-test-strip-product-insert-eua.pdf
“If this is indeed the test mentioned in the press release, it is NOT a PCR test, rather an antigen (i.e. a viral protein – specifically the nucleocapsid protein) test, which is why it is so quick – 12 minutes is what the manufacturer also states.
“These types of rapid antigen tests have been used for years for other respiratory viruses like influenza and RSV – and are of variable sensitivity. They perform better on samples with high viral loads – such as those taken early in infection, and in children who usually shed more of those viruses for longer. Generally better results are obtained when such kits are assessed/tested by laboratory-trained personnel, as is usually the case when generating these product specifications.
“But the press release seems contradictory in places saying that it offers in-store same day test results – but later, a 48 hr result when the swabs are sent elsewhere for testing. Similarly it says that it can be used for pre-flight screening – but then later on, states that it is not currently approved for this, as pre-flight testing must be done using a PCR-based assay.
“Regardless, from the limited data shown in their test specification, the test seems reasonably sensitive and specific compared to a reference PCR test: https://www.lumiradx.com/assets/pdfs/covid-19-antigen-test/sars-cov-2-ag-test-spec-sheet-us.pdf, though no details of this reference PCR assay is given – and of course the operator of this test may limit its performance if performed in-store.
“The manufacturer has also performed an impressive list of cross-reactivity/interference testing to check for any causes of false positive/negative tests in the presence of other respiratory viruses/bacteria, drugs, and body fluids:
https://www.lumiradx.com/assets/images/new/pdf/sars-cov-2-ag-test-strip-product-insert-eua.pdf
“So, just based on the data supplied in their LumiraDx manufacturer product specifications, its performance appears to be as good if not better than other similar rapid antigen tests for other respiratory viruses like influenza and RSV – at least on paper.
“However, some additional evaluations should really be performed in a real-life, in-store situation to confirm this level of performance. This is normal for any newly introduced laboratory diagnostic kit.
“So one way to do this is for an extra swab to be taken (with patient consent) at the same time as that taken for testing using the LumiraDx test, to be sent to a local laboratory with an approved in-house PCR-based COVID-19, for testing in parallel, to compare the performance of the LumiraDx against this other ‘PCR gold standard’.
“In this way, the performance of the LumiraDx can be assessed in a real-life, everyday situation.”
All our previous output on this subject can be seen at this weblink:
www.sciencemediacentre.org/tag/covid-19
Declared interests
Dr Alexander Edwards: “No COIs.”
Dr Julian Tang: “As a professional clinical virologist, our diagnostic laboratory performs assay evaluations regularly, and I advise clinical teams and GPs on the performance characteristics of such assays, and how their results are interpreted to assist with patient management.”