PCR vs. Rapid Test: When is it Better to Use a Rapid Antigen Test? - VITAL+ Pharmacy

Are over-the-counter rapid antigen tests the best way to slow down the spread of COVID-19? Here’s how to use them effectively and to your advantage.

Now that rapid antigen tests are readily available to buy in pharmacies all over the country, these quick and effective testing kits are quickly becoming the preferred mode of testing when it comes to detecting COVID-19. Particularly in light of the recent government announcements which confirm that follow-up PCRs are no longer required with positive RAT results.

So which test do you really need — a PCR or RAT? Here’s everything you need to know about taking rapid antigen tests, when and if you need to isolate, and how to ensure you get the most accurate results from your test.

What is a rapid antigen test?

Rapid antigen tests, or RATs, are at-home testing kits that detect traces of the Coronavirus. Using either a nasal or saliva swab, they detect specific proteins, known as antigens, from SARS-CoV-2 — the virus that causes COVID-19.

The swab (which is taken from inside your nose and/or mouth) reacts to a solution and detects whether or not that particular protein is present.

Unlike PCR tests (or polymerase chain reaction tests), that are carried out at either a drive-though or testing clinic, RATs can be bought over-the-counter at pharmacies, and they can be self-administered at home, with almost instant results. It can take as little as 10 to 20 minutes to get your results, compared to PCRs, which can take between 24 to 48 hours to receive results.

What’s the difference between RATs and PCRs?

Where RATs test for proteins of the virus, PCRs instead test for genetic material from the virus. These tests can only be administered by trained health workers, and samples are sent to a lab to be processed by trained technicians, as opposed to RATs, that can be self-administered anywhere.

PCR samples include both saliva and nasal swabs, which are then sent to a laboratory for testing. These tests then check to see if the sample matches the coronavirus’ genetic code — it can pick up the smallest fragment of the virus, even if it’s already dead, making them almost 100 per cent accurate, compared to RATs, which range from 80 to 95 per cent accuracy.

Your results do however take longer to come through. A PCR generally takes 24 to 48 hours to receive results, compared to RATs, which usually take between 10 and 20 minutes for your results to come through.

How accurate are RATs?

Any RAT approved for use in Australia must have an accuracy rate of at least 80 per cent (there are varying RATs ranging from 80 to 95 per cent accuracy). Whilst this does makes them less accurate than PCRs, the added benefits of a RAT is the convenience to administer yourself, and the fact that you’ll receive your results much quicker, meaning you don’t have to stand in line for hours waiting for a PCR.
It’s worth noting, however, that RATs can at times, deliver false negative results.

Rapid antigen tests are, on the whole, less sensitive than PCRs, and therefore less likely to pick up very early infections compared to a PCR, which has the ability to pick up the smallest trace of the virus, even before any symptoms start.

If you use a rapid antigen test, you’re more likely to receive a false negative (when the test indicates you don’t have COVID-19, when you actually do), or a false positive (the test says you have Covid, when you actually don’t).

This is because it takes time for coronavirus to develop in the body, so a negative test doesn’t necessarily mean you won’t test positive later on, it just means you’ve tested too early for the RAT to detect any antigens at that particular time. There’s still a chance you could have contracted the virus, which also means you could still be potentially infectious — transmission can take place 1 to 3 days before any symptoms appear.

If you know you’ve been exposed, it’s advised to keep testing with RATs until you know you are out of the infectious stage — the most infectious period is thought to be 1 or 2 days before any symptoms show, and the first 7 days after symptoms start.

Although people can be infectious for longer. NSW Government state that you can still develop COVID-19 for 14 days after you’ve been exposed. Most people who develop COVID-19 will get it in the first 7 days, so this is when you are at highest risk, but 25% of cases will develop COVID-19 between day 7 and 14, so you are at risk for up to 14 days.

So if RATs are less accurate, why use them?

Whilst RATs aren’t considered as accurate as PCRs, they are extremely effective at picking up whether you are in the infectious phase — RATs work better on symptomatic people because they are more effective at detecting high viral loads.

They become more accurate if you take the test as soon as you display symptoms or within seven days of a potential exposure, so it’s a good idea to use RATs before attending any large gatherings or before coming into contact with any vulnerable people.

The government has also announced this week, that if you take a rapid antigen test and it comes back positive, you won’t need a PCR test to confirm your results. If you get a positive result, you begin your seven-day isolation period from the day you receive your positive result. You can follow the government guidelines for further information.

They’re also a much quicker and more convenient way to test for results — RATs provide results in under 20 minutes, rather than waiting a day (or hours in line at the testing clinic) for PCR results. This makes it much easier to identify COVID-19 cases, so you can take the necessary precautions to avoid passing on the virus to anyone else.

In Australia, there are over 15 RATs approved by The Therapeutic Goods Administration (TGA), and each have been categorised according to their clinical sensitivity — acceptable sensitivity, high sensitivity and very high sensitivity.
You can see view the full list and purchase your preferred RAT here.

Some of the RATs in the ‘very high sensitivity’ category are almost equivalent in terms of sensitivity to a PCR in picking up the virus. So, the greater the sensitivity of the test, the better the chance it has at detecting COVID-19, and the less chance it will deliver a false negative.

You may also qualify for free rapid antigen tests. If you hold an eligible Commonwealth concession card, from 24 January, you can access up to 10 free RATs over a 3 month period at community pharmacies. You can read more about free RATs at the Australian Government Department of Health.

When should I use an RAT instead of a PCR?

Many of the PCR testing clinics across the country are currently at full capacity, meaning you might have to wait hours in line for a PCR test, which isn’t ideal if you’re feeling unwell, or if you don’t have the time. Taking a rapid antigen test delivers much quicker results, plus, it also cuts down the risk of you contracting

Covid whilst you’re in the testing queue — PCR testing clinics are considered high risk due to the amount of people with the virus standing in line.

If you’re a little confused as to which test you should take and when, here are some useful examples of when you should opt for a rapid antigen test over a PCR:

1. You don’t have symptoms but you want to check for sure.

Whilst you might consider a precautionary test essential, unless you’ve been a close contact of someone with a positive Covid test, or you are displaying symptoms, you may not need to take a test at all. If you are taking the test for precautionary measures, the government are currently advising people to take rapid antigen tests instead of PCRs.

2. You’ve been a close contact of someone with Covid.

If someone informs you that you are a close contact of someone with Covid, you should monitor for symptoms, then if symptoms occur, take a rapid antigen test (RAT) immediately. Should you receive a positive result, you will then need to isolate for 7 days. Close contacts are assessed based on high and low risk factors. Visit nsw.gov.au to assess whether you are a low or high risk, and what you should do.

3. If you’re travelling interstate.

Testing requirements for domestic travel has recently been revised by a number of States and Territories. Rapid Antigen Tests are now accepted if a pre-departure test is required. You’ll need to check the conditions for the State or Territory you’re travelling into before departure —you can check the full list of restrictions here — and check the latest travel advice for your destination before you get to the airport. These guidelines are constantly changing, so it’s a good idea to keep looking at health.gov.au for the most up-to-date information.

4. If you’ve arrived from overseas.

From 23rd January 2022, fully vaccinated Australians returning from overseas will have the option of completing a rapid antigen test (RAT) within 24 hours before their flight, rather than having to take an expensive PCR test within three days, which is the current requirement. Currently, PCR tests from private clinics can cost anything from $150 to $300 per person, while RAT tests can cost as little as $15. Visit health.gov.au for more information.

5. Before attending a large gathering event, or before visiting vulnerable family members.

To keep vulnerable family members safe, it’s a good idea to take a RAT for peace of mind that you are not contagious with the virus. Similarly, if you’re planning on attending a large event or gathering, you can take a quick RAT to test for Covid before you attend.

6. If you’re too ill to make it to a PCR.

If you’re experiencing any Covid symptoms and you’re too ill to leave the house, it’s better to avoid heading outside and potentially spreading the virus. Instead, arrange for a RAT to be sent to your home, so that you can test without the worry of passing it to anyone else.

7. Before you go to work.

Lots of organisations are providing employees with RATs, particularly in office environments where people work in close proximity. Regular testing means employees can feel safe in the workplace, and helps to reduce the chance of spreading.

How to get accurate RAT results

There are a few things to consider when taking a rapid antigen test.
To ensure you get the most accurate results, you should:

  • Always follow the instructions on the packaging. Each test is different, so read the instructions thoroughly before you take the sample. If you don’t use the test properly it can produce incorrect results. Here are some videos to help get you started.
  • Check the test’s expiry date.
  • Some tests require certain temperatures, so check this in the instructions beforehand.
  • Avoid contaminating the sample. Use clean, sanitised hands and do no touch the soft swab that inserts into your nose or mouth. Follow the instructions as to how you handle the test meticulously.
  • Stick to the specified time — if you wait too long, the result may no longer be accurate.
  • For saliva tests, do not eat eat, drink, smoke, brush teeth, or chew gum for 30 minutes before collecting saliva.
  • For nasal swabs, blow your nose before collecting the sample.

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