A rapid antibody test will have limited use for telling the public whether they are safe against COVID-19 infection, researchers warn today.
A major UK study reported in The BMJ says the test is useful for population studies – but flawed as a way of telling people whether they have protective antibodies.
The research involved the Abc-19TM rapid fingerprick test.
Researchers at the Universities of Bristol, Cambridge and Warwick tested samples from 2,847 key workers. 268 had previously tested positive for infection with PCR tests.
The found that 2.1% of users of the antibody test incorrectly tested positive for previous infection while the sensitivity of the test fell to 84.7% among those whose previous infection status was unknown. This compared with 92.5% among those who had previously had positive PCR tests – suggesting they might have had higher antibody tests than others as a result of having clinically identifiable disease.
84.7% sensitivity is probably a “realistic” estimate of how the test would perform in the real world, they say.
Even laboratory staff often struggled to agree whether a result was positive or negative, they said, suggesting that home testing kits might lead to even more uncertainty.
The researchers say the study “highlights the scope for overestimation of SARS-CoV-2 antibody test sensitivity in other studies in which sensitivity has been estimated only from PCR confirmed cases.”
Writing in the journal Dipender Gill, of Imperial College, London, says the work “identifies notable limitations of the UK government’s antibody test of choice and provides good evidence that its specificity in a “real life.”
Dr Gill writes: “A clear message must be communicated to the public that positive results from these assays do not provide evidence of immunity.
“Apart from limited surveillance to estimate the proportion of a population that has been infected, widespread use of this assay in any other role could risk considerable harm.”
Accuracy of UK Rapid Test Consortium (UK-RTC) “AbC-19 Rapid Test” for detection of previous SARS-CoV-2 infection in key workers. BMJ 12 November 2020
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