17 Apr 2020

Covid-19: How far away is blood testing?

3:52 pm on 17 April 2020

Blood testing is the next step in keeping track of Covid-19 but New Zealand does not yet have a test that is accurate enough to tell if a person could be immune.

A lab technician holding blood tube test.

A lab technician holding blood tube test. Photo: 123rf.com

Around the world, countries are beginning to test people en masse to see if they have been exposed to the virus and if they have developed any defence.

This can be done by blood testing - also known as serology or antibody testing.

By testing the blood, it could allow you to see where the virus had been, and where it might go in the future.

It could give accurate data into who in the community had been exposed.

You could see if a person has developed the antibodies - proteins in our immune systems that fight off bad bugs. If the blood had the antibodies, then you would know they had been exposed.

Serology testing has an important role in understanding both an individual and population response to Covid-19, said Dr Michael Dray, president of the Royal College of Pathologists of Australasia.

It can map out individuals who might have some immunity, he said.

"That may then allow us to determine that yes, they are immune.

"It may then allow us to decide that they're less likely to be infectious and also allow us to make decisions about return to work."

Dray said serology testing could also tell health officials about different groups within the population.

"It gives us a sense of the background or underlying infection; it gives us a number to use as an overall infection rate of a community or a population of people.

"And with that number then we can then get a better sense of how many people were asymptomatic how many people didn't have symptoms and required testing."

  • If you have symptoms of the coronavirus, call the NZ Covid-19 Healthline on 0800 358 5453 (+64 9 358 5453 for international SIMs) or call your GP - don't show up at a medical centre

Dray said the data was also useful to work out true hospitalisation and death rates of the virus.

Internationally there was huge interest in a simple blood test which produced results quickly and only required a prick of the finger.

But Auckland University senior lecturer in immunology Dr Nikki Moreland said it was not accurate enough for New Zealand to use.

"There are a number of tests being developed around the world, but they've been developed incredibly quickly.

"And in contrast to antibody tests for a lot of other infectious diseases, they haven't yet been through the proper assessments and validation for accuracy yet."

Moreland said by using antibody testing, New Zealand could get clean data on exactly how many people had been exposed and may have been asymptomatic.

"I think the Ministry of Health would be considering down the track, that using these antibody tests, once we know that we have tests that are accurate enough for the job, would be an excellent way of going out into the community and working out who has seen the virus, and some of those people could well be people who were asymptomatic and didn't realise they had been exposed."

The national lab, ESR said they were working to get blood samples from people who had tested positive for Covid-19 in order to check and validate different serological tests.

These tests are not useful for diagnosing someone where the virus is active.

Epidemiologist, Professor Roger Morris said they are only helpful retrospectively.

"It takes at least two weeks after a person is infected before they develop those antibodies and can be positive for that test.

"Therefore, it's no use for detecting people who have just become infected, it's only useful for detecting people who were infected two to four weeks ago,"

Morris said the virus was still a bit of a mystery.

There isn't enough information to understand if exposure to Covid-19 gives you some defence against getting it again.

"It's not yet clear whether people who have been infected once are immune for quite a short time, or immune for life or something in between.

"We simply don't know the answer to that yet. And it will take quite a while to determine it."

Serology testing is crucial in getting that information which is vital to developing and trialling a vaccine, said Morris.

But for now, the immediate response remains identifying, testing, and tracing current cases.

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