Summary

• The most common COVID-19 tests measure whether you have the SARS-CoV-2 virus, which causes COVID-19 infection.
• SARS-CoV-2 is one of a family of coronaviruses that cause respiratory infections.
• There are different ways of testing and the best known are rapid antigen tests (RATs) and the polymerase chain reaction (PCR) genetic test. 
• SARS-CoV-2 serology tests are available but are limited in their use. These look for the antibodies your immune system makes in response to the virus or vaccination.

Testing for COVID-19

Most people check to see if they have a COVID-19 infection by doing a rapid antigen test (RAT) at home. If you have a positive RAT result, contact your doctor who might suggest you have a polymerase chain reaction (PCR) test.

RATs

These tests are useful if you need a quick result. They are commercial test kits that can be bought in pharmacies and supermarkets and are made free to concession card holders in some states. They can give a result within 10-30 minutes.

How RATs work

Antigens is the name given to molecules on or close to the surface of viruses that are recognised by our body’s immune system which then makes antibodies to fight them. These tests work by detecting some of the SARS-CoV-2 antigens in the same way as our immune system does. Many of the commercial test kits detect two or more different antigens. 

Having the test

Sample

Nose (nasopharyngeal) swab.

You need to swab the inside of your nose carefully to pick up samples of mucus. It's important to follow the instructions on the packet to get an accurate result.

Any preparation?

None.

Your RAT results

Although convenient, RATs have their limitations. Their accuracy is not as good as the PCR tests performed in the laboratory. They can produce false negative and false positive results. The chance of getting a false positive result is low and a positive result usually indicates a real infection. RATs are generally best used within the first seven days after your symptoms appear.

False negatives and false positives

You may come across these terms when COVID-19 testing is being discussed.

• If the test gives a negative result in a person who is actually infected that is a false negative. 
• A person who does not have the infection but whose test gives a positive result is a false positive.

A single negative test result cannot rule out infection. This means if your RAT result is negative you need to take another one 48 hours later if you continue to have symptoms. This gives a higher chance of accuracy. You can take a third test if you are still getting a negative result with symptoms, or you can arrange to have a PCR test.

PCR testing

PCR testing detects the genetic material of the SARS-CoV-2 virus, and it is very accurate – more accurate than taking a RAT. To have a PCR test you will need to ask your doctor for a Medicare referral. You can get a PCR test at either a pathology collection site or a GP respiratory clinic.

A swab will be taken from the top of the inside of your nose or the back of your throat. Your sample will be transported to a laboratory for testing.

How PCR testing works

The SARS-CoV-2 virus is made up of a genetic material called RNA which is surrounded by proteins and fats. When the virus enters the cells in your body it uses the RNA to copy itself and produce many new copies.

PCR testing looks for DNA, another form of genetic material. This means the first step in the testing process is to convert the virus’ RNA into DNA and then use chemicals to increase the amount so it can be more easily detected by the PCR instrument.

Having the test
Sample
Nose (nasopharyngeal) swab: this is the most common way of being tested. A swab is carefully inserted into your nose (both sides) to pick up samples of mucus.  

Throat (oropharyngeal) swab: this will take samples from around the tonsils and the back of your throat.

Any preparation?
None.

Your PCR results

PCR testing can only tell if you have live or very recently dead virus in your body when you give the test sample. After you recover and the virus starts to clear, the PCR test results will  be negative. Timing is important. If the sample for a PCR test is taken too soon after you have been exposed to the virus, the viral load may not be high enough to be detected. On the other hand, doing a test when you have recovered will give a negative result.

Antibody (serology) testing

When your body is infected by a virus, your immune system makes antibodies to fight it. Antibodies to SARS-CoV-2 are made over the days and weeks following infection. The same thing happens when you are vaccinated. Antibody (serology) testing does not detect the SARS-CoV-2 virus, but it looks for the antibodies in a sample of your blood that your immune system has made to the SARS-CoV-2 virus.

Having the test
Sample
Blood.

Any preparation?
None.

Your antibody test results

Antibody tests are limited in their use. The body takes time to produce antibodies against the virus which means that these tests are very likely to give a false negative result in the first few days of infection. One problem is that we also produce antibodies against other similar coronaviruses such as the common cold and these can be detected by antibody tests and give false positive results.

Predicting immunity

A positive SARS-CoV-2 antibody test result does not necessarily mean you are immune or have immunity that will prevent COVID-19.

Antibody test results cannot be used to decide if you need a COVID-19 vaccine or booster, or to decide whether your vaccine worked. They cannot tell you whether you can infect other people with SARS-CoV-2. 

Is your COVID-19 test accurate?

The accuracy and precision of pathology tests performed in the lab are typically very good. If you do the same test multiple times on the same sample, you will generally get the same answer.

However, there is no such thing as a perfect test – one that correctly answers the question being asked 100% of the time. Many factors come into play, and not all of them are obvious.

What matters to test accuracy?

The most important thing in the case of COVID-19 PCR testing is the sample swab. Swabs that do not reach a part of the nose or throat where the virus is will not come back negative. Repeat testing should always be done on a fresh sample.

Sensitivity and specificity

Tests are usually described in terms of their sensitivity and specificity. Developing laboratory tests is a balancing act. Tests need to be sensitive enough to detect the virus at low levels, but also specific enough not to give a positive result in response to something else such as another virus.

A test that is too highly sensitive will pick up people who have the virus but may also give positive results for people who don’t have the virus. A test that is too highly specific may miss people who have the virus. 

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

More information

Pathology and diagnostic imaging reports can be added to your My Health Record.

You and your healthcare provider can now access your results whenever and wherever needed. Get further trustworthy health information and advice from healthdirect.