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Feb 1, 20214 min read

How Reliable Are Rapid Covid Tests?

Updated: Feb 5, 2021

A Dangerous Misunderstanding?

Why wrongly using the results of Lateral Flow Tests,

could be spreading COVID even further



If you took 100 people with COVID-19, the Lateral Flow Test might only correctly identify 48 of them. 52 people could be told they didn't have COVID, when they did.









The Government has spent nearly £1b buying 380m tests from US company, Innova. Understandably the government is trying hard to ensure that people can get back to work, see their families and access crucial services, as soon as possible. A test which, on -the-spot, could tell if someone had COVID, would be an enormous help in achieving that.


If such rapid tests worked reliably, it would mean that children could be tested at the school gate and if they were negative, allowed into normal classes. Families could be tested at care homes to see if they could visit relatives. People at work could be tested before they went into the office or factory and only allowed in if they were given a clean bill of health. A test which could be done in minutes would enable all of this to happen.


It would be an amazing boon for both the country’s health and wealth.


So, you can understand the excitement of lateral flow tests, which apeared to offer all this. No wonder the government spent so much money on them and loudly hailed them as a success.


But this is not only not the whole story, it is in some cases perhaps dangerously misleading.

The British Medical Journal said: “The government has claimed that rapid lateral flow covid-19 tests, which are being used in mass testing pilots in England and can provide results in 30 minutes, are “accurate and sensitive enough to be used in the community,” after evaluation results were published.


However, experts warn that the tests may miss as many as half of covid-19 cases, depending on who is using them—making them unsuitable for a “test and release” strategy to enable people to leave lockdown or to allow students to go home from university.[1]


The University of Liverpool[2] carried out research, which led to the city’s Health Protection Board suspending the use of Innova Lateral Flow Tests in allowing access to care homes, because of concerns over their accuracy. The study aimed to understand the difference in accuracy of tests which were being supervised by trained military staff and those which weren’t.


It found self-administered lateral flow tests had a sensitivity (true positive) of 48.89%[3]. It’s not an easy number to understand for most of us but in plain English it means for every 100 people with COVID it would only detect 48 of them. 52 people would therefore be told they had a clean bill of health when they didn’t. As a result, they could be wandering around unknowingly spreading the disease even further, incorrectly believing they were fine.


The counter argument is that if the tests catch anyone at all – that’s better than nothing. That is true to an extent, as long as everyone behaved as if they had COVID even if they got a negative result. But I can’t believe that is how people actually behave. We hear that many people who know they have COVID are not isolating. So how many people would keep their distance if they had just had a government approved test to tell them they are well?


This is a question about both science and messaging. It is ironic that at a time when the war time messaging of Keep Calm and Carry On, is now celebrated with tea towels, mugs and T-shirts, this latest war on COVID seems to have some very poor messaging indeed.


Jon Deeks, a professor of biostatistics at the University of Birmingham spoke to me for my investigation for ITV's Tonight programme. I put to him the government's view that

the data showed that the rapid tests worked particularly well in Liverpool and were a major factor in bringing down infection rates there.


"Well, the Liverpool report didn't actually state that or conclude that. The rates were going down anyway, and they didn't seem to be a steep change in the decline rate. And there was no real difference between the rate in Liverpool and in surrounding areas. So I don't think that the data or the conclusions of the report said that the politicians certainly did. And it certainly hasn't had a long term benefit in Liverpool."


His own study of the effectiveness of Lateral Flow Tests were even worse than the research conducted at Liverpool University. He told me:


"So our evaluation in Birmingham was a shock to me. We tested seven thousand one hundred students before they went home...we missed 97 percent of the students who would have been positive on PCR. That was a shock. That's that's a very, very bad rate."


Despite the concerns raised by the Birmingham and Liverpool studies, politicians seem to be either ignoring or dismissing them.field I spoke to Lord Bethel who is the Parliamentary Under Secretary of State for Innovation and leads on COVID -19 policy areas including:

  • supply (medicines and testing)

  • treatments and vaccines

  • long-term health impacts

  • test and trace: testing, trace, technology

But despite his key role in this area of national crisis, he seemed unaware of concerns raised by the Liverpool and Birmingham studies when I asked him about them. He told me:


"No, I don't recognise those figures. They found eight hundred and seventy four positive tests in in Liverpool. That's an amazing achievement. Those are people who were out in the community, had no idea that they had the infection, were potentially giving the disease to the people that they love and work with."


There is no doubt that the rapid lateral flow tests are potentially helpful if used correctly. They provide an important scientific breakthrough. There is nothing wrong with the tests themselves, but it's equally important to understand that we must be very careful in how we respond to the results they provide. Not properly understanding what the results are telling us and not behaving responsibly, may have potentially harmful implications.


This is a time when confusion is dangerous and the government must give the right words and the right message to explain the right science.




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