• 01 Jun 2020
  • 8 min 06
  • 01 Jun 2020
  • 8 min 06

The advice from Australian health authorities around testing has been evolving as the COVID-19 situation evolves. And as with everything to do with COVID-19, even the available tests are new, with the data growing all the time.

In this episode, NPS MedicineWise medical adviser and GP Dr Anna Samecki interviews fellow medical adviser and GP Dr Jill Thistlethwaite about how clinicians can practice quality use of testing during this pandemic.

Transcript

Voiceover:

Welcome to the NPS MedicineWise podcast, helping health professionals stay up-to-date with the latest news and evidence about medicines and medical tests.

Anna Samecki:

Hello and welcome. My name's Anna. I'm a medical advisor at NPS MedicineWise, and I'll be your host for today.

I'm joined by my colleague, GP and fellow medical advisor, dr. Jill Thistlethwaite. Hi, Jill.

Jill Thistlethwaite:

Good day, Anna. Nice to speak to you again.

Anna Samecki:

Yeah, nice to speak to you too. Can you tell our listeners a little bit more about yourself?

Jill Thistlethwaite:

Yeah. So as you mentioned, I'm a GP. I work in Sydney, and I've also been a medical advisor at NPS MedicineWise the last four years. I'm also a health professional educator.

Anna Samecki:

Great. Thanks, Jill. So moving straight into it, the advice around COVID testing has changed with time, and the latest advice from Australian health authorities has been to pretty much test everyone and anyone with symptoms consistent with COVID-19.

At the moment, the two broad categories of tests available are PCR tests, also known as nucleic acid amplification tests, and serology or antibody tests. Unfortunately, reliability remains one of the main concerns. So our aim today will be to focus our discussion on the quality use of these tests. So Jill, as a GP, what does the quality use of tests mean to you?

Jill Thistlethwaite:

Well, for me, it means thinking before deciding to do a test, what is the clinical question that this test will help me to answer or will help the patient have an answer for? And then related to that is how might the test result affect management of this patient? So when we think of the two tests that you've mentioned related to COVID-19, those are the questions that I'd be interested in asking before thinking about doing either of them.

Anna Samecki:

Well, I certainly agree with that sentiment. So focusing now on the PCR tests, these are the mainstay of COVID-19 testing at this time. Can you walk us through why we're using this method and what we should be telling patients?

Jill Thistlethwaite:

Yeah. So PCR testing, as you say, is what we're using in Australia to answer the question, "Does this person, does this patient have an acute COVID-19 infection?" So the PCR test is a diagnostic test. And as most people are now well aware, it's taken by doing nasopharyngeal and oropharyngeal swaps to look for the presence of viral RNA. And the test is useful to diagnose an acute infection during the first 10 days of symptoms, but also it can be used in asymptomatic patients who've been in contact with a person with COVID-19.

Anna Samecki:

Can you tell us how reliable these tests are?

Jill Thistlethwaite:

Well, we've been thinking that the swab tests are quite sensitive and that if you have a positive COVID-19 test, you usually presume that you have got COVID-19. However, there has been some doubt raised recently about sensitivity. So as with any test, it's never 100% reliable, so have to put the test results that you get for a particular patient in the context of the symptoms that that patient has.

So if you've got a patient with symptoms that are suggestive of COVID-19, and there are quite a number of these now as we know, and the test is positive, then it's highly likely that this patient has got COVID-19. If the test is negative, then you may still want to manage the patient as if they have COVID-19. So it's always done on the basis of the patient that you have sitting in front of you or that you've spoken to through telehealth. So these aren't quite as good as I think, as we have been led to believe.

However, obviously it also depends on how well the swabs have been taken. Has the swap got into the right place? And also how well the test sample has been transported to the testing laboratory. So there's another number things that can affect the result there.

Anna Samecki:

Yeah, that's a great summary, Jill. I mean, we don't manage the test result. We manage the patient, and we certainly have to always interpret the test results in the context of the patient presentation, so that's really good.

Moving on to serology tests now. I mean, that's another potential option available. And we do know the TGA's approved over 50 point-of-care tests for use in Australia. So what can you tell us about those?

Jill Thistlethwaite:

Well, this is a much more controversial area as you're aware. So if we go back to considering the clinical questions that we're trying to answer with serology or antibody testing, and thinking of that in the wider sense of any serology that we do for viruses, the first question when we're choosing a serology test is: Does this person have an acute infection? So what is the diagnosis?

An antibody test for COVID-19 is not recommended for acute diagnosis. As I just mentioned before when we discussed the test for diagnosis is the PCR. The antibody test will not show any response for at least about two weeks after an infection, and therefore it cannot be used as an acute diagnostic test.

Anna Samecki:

That's very interesting, isn't it?

Jill Thistlethwaite:

I think it is very, and this space is changing all the time as you are well aware. The question we ask when we're looking at serology is, is this person immune? And in this case, is this person immune to COVID-19? Well, the answer to that is clear for what I was just saying about the difficulty of interpreting the antibody tests for COVID-19. There is no way of knowing if the patient is immune with an antibody test at the present time. We don't know what the antibody level should be for immunity. And if there are antibodies, conferring some immunity on a patient, we don't know how long that that immunity would last. So these tests are not useful and should not be taken as a reason for a person to stop social distancing.

Anna Samecki:

Certainly agree with you there, Jill. So in summary, can you tell us the main takeaway messages for health professionals about testing in a few sentences?

Jill Thistlethwaite:

Consider the clinical question you're trying to answer. For acute diagnosis of COVID-19, refer for a PCR test. Tests for antibodies at the moment have no real place in clinical practice, but they may do in the future.

Anna Samecki:

Fantastic, that's very clear and concise. Thanks, Jill. So thank you all for joining us today. Further information is available on our NPS MedicineWise COVID-19 hub. And if you have any questions about or suggestions for our podcast, please send them through via Twitter or LinkedIn. Thanks again for listening.

Voiceover:

For more information about the safe and wise use of medicines, visit the NPS MedicineWise website nps.org.au.