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How testing works for COVID-19

8 October 2020

COVID-19 is the disease caused when a person is infected by a new coronavirus called SARS-CoV-2.

There are two kinds of tests that can detect whether a person has been infected with SARS-CoV-2 and has the COVID-19 virus.

  1. Tests that detect the presence of the actual SARS-CoV-2 virus in your body. This is usually done by testing if the virus is present in your throat, nose, nasal secretions (snot) or sputum (saliva/spit).
  2. Tests that detect whether your body has produced antibodies to the SARS-CoV-2 infection. This is usually done by taking a sample of your blood and testing your blood for specific antibodies.

Detecting the presence of SARS-CoV-2 virus

Two types of tests that detect the presence of the SARS-CoV-2 virus include - nucleic acid tests that detect the virus’s genetic material and antigen tests that detect specific viral proteins.

Nucleic acid tests

These tests detect the presence of the genetic material, called nucleic acids, of the actual SARS-CoV-2 virus. Such tests are good at detecting the virus early in the infection and can sometimes even detect the virus in a person before they become unwell. There are several types of nucleic acid tests that can be used to detect the SARS-CoV-2 virus, including polymerase chain reaction (PCR) tests and isothermal nucleic acid amplification tests (e.g., loop-mediated isothermal amplification (LAMP) tests).

PCR tests are generally considered better at detecting the presence of the SARS-CoV-2 virus and are currently the gold standard for diagnosis of COVID-19.

Nucleic acid tests are complicated to do and usually need specialist scientists to run the tests in a laboratory to get an accurate result. The laboratory scientists can sometimes run these tests on automated machines that can do many tests at once. This means that you can test lots of people quickly.

There are now some SARS-CoV-2 nucleic tests available that can be used outside of a laboratory by trained people. Most of these systems give results quickly but cannot do many tests at once.

Rapid Antigen tests

These tests detect the presence of specific proteins of the SARS-CoV-2 virus in symptomatic patients. Rapid antigen tests can be performed by health professionals outside of a laboratory and may produce a result within 15 30 minutes, although their ability to detect the virus may not be as good as a nucleic acid test.

Rapid antigen tests are generally best performed within the first 5-7 days from the time symptoms first appear. Negative results, and some positive results, may require further testing by a nucleic acid test to confirm if a patient is infected with the SARS-CoV-2 virus.

Rapid antigen tests, are not intended for home testing. They are designed to be used by trained health professionals or laboratory scientists.

Detecting antibodies to the SARS-CoV-2 virus

These tests look in our blood to see if our body has started fighting a SARS-CoV-2 infection, rather than detecting the actual SARS-CoV-2 virus. They do this by seeing if our blood contains specific antibodies that attach to parts of the virus.

It takes time for our bodies to make antibodies, so people can already have the SARS-CoV-2 virus and be spreading the infection to other people before we can detect their antibodies.

Scientists usually run viral antibody tests in laboratories, however since the beginning of the COVID-19 pandemic, a number of manufacturers have developed tests that can be used outside of the laboratory at the point of care. These are called rapid or Point of Care tests (PoC or PoCT). You might also hear these tests called IgG or IgM tests. IgG and IgM are different kinds of antibodies that are made by our bodies to fight infection.

These rapid and PoC antibody tests are not intended for self-testing. They are designed to be used by a health professional.

Important things to remember

It is illegal for someone to sell you a test claiming that you can test yourself for a COVID-19 infection. In Australia, the supply of self-tests (i.e. home use tests) for COVID-19 is prohibited under the Therapeutic Goods (Medical Devices—Excluded Purposes) Specification 2020.

As you can see from the above information, it is complicated to accurately detect a SARS-CoV-2 infection. This is why we need to make sure that all COVID-19 testing is done with a health professional. The health professional can provide you with appropriate advice and treatment if required, and importantly, the health professional can alert the relevant health authorities. This way we can trace infections and take action to stop further spread of the infection.

Please see the Department of Health website for all COVID-19 updates.

The TGA will take action in relation to any report of poor or faulty performance of these devices. Reports can be submitted via the TGA website.