One of the first medical experts to trial the latest test in the Covid-19 toolkit explains how rapid antigen tests are used and whether they are accurate.
Middlemore Hospital Emergency Department. Photo: Stephen Forbes / Stuff / LDR
Rapid antigen tests will play an important role in the future fight against Covid-19, and it's critical the country is prepared.
That's the view of a technical advisory group on testing for the virus, which released its report yesterday.
Middlemore Hospital in South Auckland was the first to trial rapid antigen tests, or RATs, and its chief medical officer Pete Watson told Morning Report how the tests are used.
"We were the first people to trial this and we've been learning as we go about how to use it ... what happens is that a person would have a nasal swab, the swab doesn't have to go as far back as the PCR test so it's a lot more comfortable. (It) sits in the front of the nose, gets swivelled around a couple of times then taken out put into a tube where it's stirred with a bit of reagent and then poured into the kit.
"The test then sits there for 10-15 minutes and then the result comes up which is a couple of lines and depending on what those lines show is whether it's a positive test or not," Watson said.
"For us, the trial has been about learning how to do it ... making sure we are doing it correctly, there may be other tests that are simpler and more straightforward."
The small test kits are similar in appearance to a pregnancy test, he said.
There are alternative RAT saliva tests on the market but the Middlemore Hospital trial had only used the nasal swab variety, Watson said.
Due to questions around the sensitivity of the new tests, the hospital was using RAT tests in conjunction with the standard PCR testing.
"At the moment, this is a test that we're doing alongside the PCR testing because we're again not sure of the sensitivity so at the same time we're doing the standard PCR tests and sending them off to the lab."
Watson said there were some discrepancies found between the results returned by the new RAT tests and the 'gold standard' PCR tests during the trial.
"We're pleased that when we have had a positive result the PCR test has come back positive, that's been our experience so we've ruled in those tests where the RAT test has turned up positive.
"But we've also had the opposite where the RAT test has turned out negative but we've suspected the person had Covid the PCR turned positive and of course that's the concern, the lower sensitive of the RAT tests."
Watson said the disparity in results demonstrated why health authorities are taking a cautious approach to rolling out new testing methods.
"It doesn't replace PCR testing and when you get a negative test particularly in somebody who is symptomatic it's very important that we continue to take the PCR testing."
"We're looking here at in the hospital setting in the emergency department but clearly when these tests get rolled out for workers, workplaces and other settings it's going to be around the frequency of the testing which is going to be a difference."
Although the addition of RATs has provided some hope for Middlemore Hospital staff, Watson said the key step to protecting patients and staff is increased vaccination rates among inpatients.
