COVID-19 rapid antigen tests are less accurate than PCR tests, but experts say they serve a purpose

When Sydney man Andrew Colagiuri developed COVID-19 symptoms, he was too ill to set up a standard swab, known as a PCR (polymerase chain reaction) test.

“My symptoms were pretty bad. I probably should have gone to the doctor,” he says.

Instead, he took a rapid antigen test (RAT), which can be done at home.

The result was negative, and after three days in bed, he was healthy enough to take a PCR test.

It eventually also came back negative, but screening delays due to high demand meant that his results did not come back for almost a week.

Meanwhile, he took another RAT test, which came back positive, and the result was then confirmed by another PCR.

A photo of Andrew, wearing a gray jacket and black shirt, smiling, with a green street and cars visible in the background.
Andrew Colagiuri said his symptoms were so bad he could not imagine standing in line for more than five hours.(Delivered by: Andrew Collages)

Sir. Colagiuri does not believe it is acceptable to expect COVID-19 positive people to line up for a five or more hour for a PCR test.

“I … could not imagine having to queue for five hours [to] try to get a test at the moment if you actually had COVID, because the symptoms were pretty severe for me, “he said.

Many experts agree and call for a national approach to RATs to help reduce the demand for the PCR test system and ensure that those who need one are given priority.

Both types of tests serve a purpose, according to Australian Medical Association Vice President Chris Moy.

“The advantage of this [rapid antigen] The test is that it’s really practical and you get the results very quickly, but its downside is that it has a much higher false negative rate, “said Dr. Moy.

“That means you can get a test result that comes back negative … but actually you actually have COVID.”

Colagiuri said he still had full confidence in using RAT tests in the future, but said it was important to do your research to find out which ones were the most reliable.

Jaya Dantas, professor of international health at Curtin University’s School of Population Health, believes the purpose of the two tests is changing now that COVID-19 is much more common in many parts of Australia than ever before.

She believes that RATs should be used in more everyday settings, while PCRs should be reserved for the most vulnerable and those who need confirmation of their diagnosis.

“When you have thousands of people in line, or you have long queues of cars where people wait for hours … it’s unbearable,” she said.

“It would be much better for people to actually get these fast antigen tests. If they test positive, then they go in for a PCR test. This will then ease the pressure on labs and people who actually perform the tests.”

How accurate are fast antigen tests?

There are currently 15 RATs approved for use in Australia.

Their approval was given by the Therapeutic Goods Administration (TGA), which has also ranked each of these tests by accuracy, with “acceptable sensitivity” being at the lower end of the scale and “very high sensitivity” being the most accurate.

Any RAT approved for use in Australia must have an accuracy of at least 80 percent.

RATs have a much lower accuracy than PCRs, but their convenience and the fact that you can typically get a result within 15 minutes are advantages.

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Jeremy Fernandez explains how to take a quick antigen test and how they actually work

But in a worrying development, the US Food and Drug Administration (FDA) has released a statement warning that the RATs used there do not appear to be as effective in detecting the new Omicron variant. Although it added, the data was preliminary.

“Antigen tests are generally less sensitive and less likely to detect very early infections compared to molecular tests,” the statement said.

“If a person tests negative with an antigen test but is suspected of having COVID-19, such as experiencing symptoms or has a high probability of infection due to exposure, follow-up molecular testing is important to determine a COVID-19 infection. . “

Dr. Moy said anyone who received a positive RAT should consider themselves COVID positive and get a PCR test to confirm the diagnosis.

A graph showing that tests with lower sensitivity are most likely to detect COVID when a person's viral load is highest.
Rapid antigen tests are more likely to detect COVID-19 under the infectious window (stained orange).(Delivered: BMJ via AMA)

He added that RATs were less reliable at capturing the disease at either the beginning or end of an infection.

“What [they are] very good at is to detect if you are in the infectious phase. That means it’s the time you want to actually excrete the virus and actually spread it to other people, “he said.

For that reason, Dr. Moy, it made sense to use RATs before going to large gatherings, or at few-day intervals for those entering areas with vulnerable people, such as elderly care and health conditions.

“If it’s negative, you’ll probably be outdoors for at least the next few hours or … maybe the next few days,” he said.

How do RATs and PCR tests differ?

Traditional PCR tests detect genetic material from the virus, while a RAT detects whether COVID-19 virus proteins are present in your body.

PCRs are still considered the “gold standard” for testing with an accuracy rate of over 90 percent.

They are also free.

The PCR test must be performed by a trained healthcare professional, who strokes a patient’s nose and throat, and the results are produced by a laboratory. This can take several hours or even several days if the system is under pressure.

RATs come in set form and you fill them out at home. They either test your saliva or require a nasal swab, although the probe does not need to be inserted as far as the PCR swab.

A result takes about 15 minutes, depending on the test mark used.

The downside is that they are not available everywhere and stocks are limited. They can also be expensive, and put them out of reach for many people.

Experts say a national approach is needed

Both Dr. Moy and Professor Dantas were critical of the lack of a coordinated approach when it came to RATs.

“I think we need a common approach across Australia with the rollout of the rapid antigen tests,” Professor Dantas said.

“What we need to see is a consistent effort across all states and territories where they are accessible to people, especially people who travel, athletes and athletes, truck drivers, people in elderly care.”

Professor Dantas also said that more needs to be done to ensure that there was justice, and suggested that governments should make RATs available at a minimal cost or for free.

Dr. Moy also worries that lack of consistency leaves people confused and frustrated, saying authorities should keep an eye on what is happening abroad to ensure Australians are prepared.

“Unfortunately, the PCR test system is overwhelmed at the moment and is becoming less useful during the whole pandemic due to the delays in being able to get a test and also the delays in getting [results] back in the moment. “

At a news conference, Prime Minister Scott Morrison said state governments were responsible for securing RATs to the public, but added that the federal government had set aside more than $ 350 million to buy additional RATs for the national stock.

He also said the TGA was evaluating other brands of RAT kits for possible use in Australia.

Meanwhile, Andrew Colagiuri is recovering and must leave his home quarantine on New Year’s Eve, though he believes another thing that could have helped his recovery was a more competitive Ashes match.

“After four or five days, you generally get well, just a lot of fatigue,” he said.

“Now I’m just bored [from] sitting at home. The cricket ended early, which was a shame, so there is not much else to do. “

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How to take a quick antigen test

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