Rapid coronavirus test missed more than half of cases, data suggests

Rapid coronavirus tests rolled out in Liverpool missed more than half of those who had Covid-19, preliminary data suggests.

A document released by the Scientific Advisory Group for Emergencies (Sage) on Friday shows the tests missed around 51% of all cases.

The paper considered by Sage on November 26 said two days earlier the Liverpool Health Protection Board had decided to pause plans to use the Innova lateral flow test to allow care home visits because they were not accurate enough.

One week later the Government started sending out the tests to England’s biggest care homes.

On December 5 the chief medical adviser to NHS Test and Trace defended the uses of the tests, despite concerns around the accuracy.

HEALTH Coronavirus
HEALTH Coronavirus

Dr Susan Hopkins said the tests had enabled them to find many cases of infection in people without Covid-19 symptoms that would otherwise have been missed.

She explained the programme was about case detection, and people with a negative test were not being told they did not have the disease.

Instead it was identifying those who do have Covid-19, and telling them to isolate.

Professor Richard Tedder, senior research investigator in medical virology, Imperial College London, said: “The data presented on the performance of the Innova lateral flow assay for detecting Sars-CoV-2 clearly indicate in this study that when compared against a benchmark molecular test such as a quantitative PCR the lateral flow test is very very much less sensitive, detecting only about half of the known positive samples subjected to testing.

“Indeed it even failed to detect two out of five samples with the highest level of viral gene copies, these displayed a PCR CT of < 20 (ie were samples which could be diluted one million fold and still give a positive PCR signal).

“This graphically shows that this assay is simply not sensitive enough to use to test persons with a view to confirming an absence of infection and thereby an absence of infectivity.

“A negative result with this lateral flow test simply does not infer an absence of infection.”

Dr Alexander Edwards, associate professor in biomedical technology, Reading School of Pharmacy, University of Reading, said: “It’s fantastic to see this Quality Assurance data published as it gives us a better understanding of the performance of these Innova rapid swab tests when used in the ‘real world’.

“It is not fantastic to see that the sensitivity vs RT-PCR drops below 50%.

“This low accuracy was mentioned in passing from a guidance document encouraging the use of this product for mass testing programmes.

“This is also rather different to the product instructions stating sensitivity of 96%.”

He added: “Great care must be taken to make safe, efficient, and cost-effective use of all testing tools available.

“The speed, relative simplicity and relatively low cost of this particular rapid test, may come at the cost of performance.

“But the more cases that are detected and helped to isolate before they can spread, the better.”