The COVID-19 test measures whether you have the SARS-CoV-2 virus, which causes COVID-19, in your body fluids. SARS-CoV-2 one of a family of coronaviruses that cause respiratory infections. There are several ways of testing and the best known are polymerase chain reaction (PCR) and rapid antigen tests (RATs). In each case, a sample or swab is taken from your nose and/or throat. The test is an essential part of the diagnosis of COVID-19 and can be used to monitor people after the initial infection.
Why get tested?
The first goal is diagnostic testing in people with symptoms. The question being asked here is: are symptoms due to COVID-19 or something else such as the common cold or flu? This is the most important question because COVID-19 is highly infectious and infected people need to know as soon as possible to prevent them transferring the infection to other people. If you have any of the symptoms that can occur with a COVID-19 infection, you should get tested.
A second reason to test is if you have been identified as being in a location close to someone who has COVID-19. In this situation, you may not yet have symptoms and you may be at the start of the infection process, but it remains important to test and see whether you are infected.
PCR (genetic) testing
Most COVID-19 tests are conducted in laboratories using polymerase chain reaction (PCR). This looks for the genetic material of the virus and is the most accurate method of detection.
This is a sophisticated test that involves several complex processes. The testing process is repeated as many as 45 times (cycles) in a PCR machine. The virus shows up as a fluorescence signal. The earlier the virus shows up in the number of cycles the greater the amount of virus (viral load). If fluorescence does not appear until the final cycles, it suggests that the person has a low viral load possibly, they have been only recently infected or were infected at some time in the past and are not carrying much virus. This can help in assessing how infectious someone is and when they became infected. Specially trained scientists are required to oversee the test and interpret results.
Rapid Antigen Tests
Rapid antigen tests known as RATs detect bits of proteins called antigens on the surface of the virus. This is a self-test that comes in a cassette form similar to a pregnancy test and can be performed anywhere. It involves applying the swab sample to a small opening on an oblong test strip and waiting a short period of time. The virus is detected by the presence of a coloured band. These are less accurate than PCR testing but they can give a quick result and are useful if you have symptoms, will be attending a large gathering or visiting someone who is vulnerable to COVID-19.
There are also antibody (serology) tests for COVID-19. These do not detect the COVID-19 virus but measure the body's response to the virus by forming antibodies. Your body makes antibodies as a way of fending off infections. When you recover from a COVID-19 infection, your COVID-19 PCR test becomes negative for the virus, but your antibody test will be positive and be a measure of your immune response. Antibody tests are widely used to manage many infectious diseases.
Having the test
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.
PCR results are usually available between 24 to 48 hours after sample collection and they are presented as being negative or positive for COVID-19.
A positive test means it is extremely likely that you have COVID-19. There are circumstances when a false positive result is given, but these are very uncommon.
If you have a negative result, you probably don't have COVID-19 at the time you took the test. However, you can still be infected but not have enough of the virus in your nose and throat to show up. This may mean you are at the start or the end of an infection. Bear in mind that the test can only measure the virus that you have in your body at the time the test is taken. You could become infected immediately afterwards. This is why it is important to be tested at any time you have symptoms.
Modern medical tests are highly sophisticated, but they cannot be 100 percent reliable. Test designers must balance many competing requirements. There is always a small chance that someone may test positive for an infection they don't have (false positive) or have an infection that goes undetected by the testing process (false negative). Sample collection plays an important role. The test cannot give an accurate result if the sample has not picked up enough of 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 themeverything you think may 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:
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