FactCheck Q&A: New Coronavirus “Blood Tests” – Channel 4 News


Health Secretary Matt Hancock says he wants to see 100,000 coronavirus tests a day by the end of this month.

New blood tests will be part of the test campaign. But these tests have already created confusion and controversy, with government officials grappling with science journalists.

Here’s what we know and what we don’t know.

What are the different types of tests?

The tests used on many hospital patients and some NHS workers are now called polymerase chain reaction (PCR) tests.

They detect the presence of RNA – the genetic material of the virus – which should tell us if someone is infected now.

But the swabs have to be taken from the patient’s nose or throat and sent to laboratories for testing, which takes time.

And independent experts told FactCheck that up to 30% of the results could be false negatives, so many patients have to be tested more than once to get an accurate result.

The new test that Mr. Hancock wants to deploy alongside the swab test is done on blood samples. He called it “the blood test,” but it’s more commonly called an antibody or serological test.

This antibody test does not detect the presence of the coronavirus itself. It shows whether the immune system has created antibodies to fight it.

The government has previously stated that it has ordered millions of kits. They are expected to be available soon, but are apparently still being assessed by the authorities.

Why do we need a new type of test?

The antibody test tells us if someone has ever had a coronavirus in the past.

Among other things, this means that key workers who have been infected with a coronavirus – perhaps without experiencing any symptoms – can return to work without fear of catching it again.

In theory, if someone has the antibodies to fight a virus, they should be immune to it in the future – at least for a while – although scientists have yet to prove if and how it might work. coronavirus.

Does the blood test show if you have a coronavirus now?

This point became extremely controversial this week when Professor Jonathan Van-Tam, Deputy Chief Physician for England, appeared on the ITV Peston show.

In a video clip that quickly went viral, Professor Jonathan Van-Tam told Robert Peston that he was wrong on science, saying, “Blood tests check if you have any. They can’t know if you have it right now. “

The reporter said, “The point about these tests is that they not only tell you if you have the type of antibody that gives you immunity, but in theory, they will also be able to significantly speed up tests of people who actually caught the virus. “

He went further in a blog on the Spectator’s website, writing that antibody tests “can be used to identify if a person with symptoms actually has the virus.”

“They would therefore constitute a cheap and effective alternative to laboratory tests that the government is struggling to step up …”

The scientists and manufacturers contacted by FactCheck have made it clear that antibody tests alone cannot provide a complete alternative to the viral tests we currently use – they can only supplement them.

The body does not produce antibodies until several days after catching the virus.

If you have an antibody test in the first few days, the result can be negative even if you have the disease.

FactCheck spoke to Biopanda Reagents, a Belfast-based manufacturer and supplier, of Covid-19 antibody test kits.

The company has produced a graph that shows how the testing process works. The first antibody, called IgM (the green line), is only detectable after several days of infection:

The immune system produces another antibody later (IgG – the red line) and this provides long-term immunity.

We can see from the graph that there is an initial period of several days where you could have the coronavirus and may have already developed symptoms – this is the blue line – but you would not be positive for the IgM antibody.

Han Yan from Biopanda told us, “I should point out that the timescale is presented only to give a very general idea of ​​the dynamics of the humoral immune response, as each person’s immune response is different.

“As you can see, there is a window period when a person can become infected and even show symptoms, but during which the antibody test will not come back positive. However, during this time, a PCR test should detect the presence of the virus.

“With all of this in mind, we would never recommend our antibody test as a means of replacing RT-PCR for the early and intermediate diagnosis of COVID-19 due to the risk of false negatives …

“So, if the antibody test is used to diagnose a current infection, it should be used with RT-PCR and with other clinical information such as lung tests. It is best to use it to provide evidence of a historical infection.

“If you want a quick diagnosis of the current infection, you ultimately need to look for evidence of the virus itself, not of the body’s immune response. “

Why use both?

Although antibody or “serological” tests may not be the best choice for early diagnosis alone, the evidence from China suggests that combining them with PCR tests can significantly improve the chances of a specific result.

A blood sample study of 173 patients in Shenzhen found that an antibody test started to give more accurate results than a PCR test after the first five and a half days of the disease.

Combining the blood test with the PCR test allowed doctors to detect 98.6% of coronavirus cases, compared to 51.9% with a single PCR test, according to a review in the New England Journal of Medicine.

The authors concluded: “Serological tests can improve the early diagnosis of Covid-19. Due to the high false negative rates with PCR, serological testing will be a useful adjunct to RNA detection. “

So some scientists think it is too simplistic to say that antibody tests cannot show a current coronavirus infection.

Dr James Gill, locum doctor and honorary clinical professor at Warwick Medical School, told FactCheck: “The best test for early infection is to combine the antibody test AND the patient’s PCR sample. “


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