27/09/2020 08:05 BST | Updated 27/09/2020 08:05 BST

'A One-Off Test Is A Folly': The Truth Behind Covid False Negative Covid Results

"The whole system is failing at the moment. And it’s happening just as the numbers of coronavirus infections are starting to rise," one expert warns.

When Sarah found herself suffering sudden bouts of breathlessness in May, she took herself to hospital.

But after her Covid-19 swab test came back negative, doctors said she was probably anxious, and sent her home.

Despite this, Sarah’s symptoms continued to worsen. A week later, she was rushed to hospital in an ambulance. Paramedics told her that based on her clinic observations, she should be in a coma.

Then came more surprising news: She had tested positive for coronavirus.

A doctor explained her first test had been a false negative – a result that comes up despite the patient having the virus, and possibly being contagious.

As a clinically vulnerable Covid-19 patient with a chronic illness, I have had frequent contact with hospitals and healthcare systems during this pandemic. I have also been told by doctors that the potential for false negative results is high, so I decided to find out if this was true.

The answer, according to the experts I spoke to for this article, is a resounding yes.

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There are concerns the rate of false negatives could increase with the introduction of rapid testing.

Sarah’s story – given to a patient safety charity under a pseudonym – is one that resonates with Dr Claudia Paoloni.

Paoloni, president of the Hospital Consultants and Specialists Association, detailed another case in which a patient tested negative twice: once when she was first admitted to hospital and once later in her hospital stay. She finally tested positive on her third test – by which time she was on a ventilator in intensive care.

“To use as a one-off test in any capacity to exclude someone from having Covid-19 is a folly.”

Paolini believes Covid-19 swab tests produce a troublingly high rate of false negative results, and the problem lies in the reliance on a single test.

“To use as a one-off test in any capacity to exclude someone from having Covid-19 is a folly.” 

If you want to exclude someone from having the virus, Paoloni said, you must do multiple tests and collect multiple negative results.

“If the test and tracing system is not working, which is the case here, transmission will continue unabated in the community.”

Paoloni also warns this could get worse as the government tries to introduce rapid testing. 

A study from Imperial College London published earlier in September put the sensitivity rate of rapid testing between 94% and 100%. That’s one in 20 people with Covid-19 who will almost definitely get a negative result.

The current rate of false negatives in the UK was originally estimated at 30%, she explained. Things have improved since then, but it’s still around 8%, she said, which is almost two in 20.

The most recent data published by the Office for National Statistics says the test’s sensitivity - which it says can tell us how likely it is to return a false-negative result, may be somewhere between 85% and 98%. 

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It's not just the quality of the test, but how it's carried out, that is causing some alarm.

Dr Steven Woloshin, the co-director of the Center for Medicine and Media at The Dartmouth Institute, decided to investigate the level of false negative Covid-19 results because he, too, was concerned about people who believed they were not infecting returning to the community. The research he published in August, he said, was borne out of worry for his elderly mother.

He believes some negative Covid-19 results should be “taken with a grain of salt”,  citing research showing that the true false negative rate could be anywhere between 2% and 29%.

But the quality of the test itself isn’t the only reason we could be getting high rates of false negatives, experts said.

Dr Deenan Pillay, Professor of Virology at University College London and member of Independent Sage, a group of scientists providing transparent advice during the crisis, said a significant number of self-administered tests could be coming back negative for people who do in fact have the virus.

“The single biggest reason why a swab from someone who has Covid-19 comes up as negative is the quality of the swab that is taken,” Dr Pillay said.

“Swabbing your nose and throat in a way that will pick up the virus means really scraping down the side of the wall of the nose or back of the throat to get cells from the lining of the throat. That’s not a pleasant thing to do.”


The way the system is developed at the moment, outsourced to private companies ... is just woeful,Dr Deenan Pilla


Pillay believes the importance of having a test administered by a well-trained professional is often trivialised, but it could be damaging our ability to contain the virus.

This is of course true for at-home testing, which relies on the patient or a family member to collect the swab. But it could be true at testing centres, too.

Tom, a 29-year-old from London whose name has been changed for this story, said there were no medical staff on site when he visited a Covid testing centre in London. The only people he interacted with were staff from a third-party contractor paid to carry out testing.

“The man simply handed me a test, read out the instructions to self-administer the test, and asked me to do it myself,” he said.

Tom believes he was unable to get a good sample due to the difficulty of the testing technique.

Pillay agrees that testing methods are likely to have an impact on false negative results.

“I have seen the documentation given out at testing centres and it is very confusing,” he said. “Centres often expect you to administer the test yourself or get someone else in your car to administer it for you, all of which creates difficulties.” 

According to figures released by the Department of Health and Social Care (DHSC), around two thirds of the 571,400 people who were newly tested for Covid-19 between September 3 and September 9 were tested either at home or at testing centres.

A spokesperson for DHSC told HuffPost: “The tests are reliable and effective according to health experts, independent inspectors and international peer reviewed evidence. This includes self-swabbing for Covid-19 being just as effective as clinician-administered swabbing.”

Pillay believes the solution lies in having medically trained staff at testing centres.

“The way the system is developed at the moment, outsourced to private companies like Deloitte and Lighthouse Labs, is just woeful,” he said.

“The whole system is failing at the moment. And it’s happening just as the numbers of infections are starting to rise,” Dr Pillay said.

Deloitte and Lighthouse Labs have been contacted for comment.