How do COVID-19 tests work?

Rajner Perpepa

From the beginning of the Corona Virus pandemic until now, it’s likely you’ve undergone some form of a test to identify if you were infected with the Corona Virus. You may have felt ill one day and thought you had the virus, or maybe you were travelling outside the country during the pandemic. Testing was a crucial process implemented into pandemic guidelines to help people quarantine when necessary, ultimately reducing the chances of the virus spreading. To understand how the testing process works, we must first ask, what exactly is Covid-19?


What is COVID-19?

COVID-19 is a transmittable disease caused by the SARS-CoV-2 virus, commonly referred to as the Corona Virus. Although we call it the ‘corona virus’ pandemic, coronaviruses are actually a group of 7 different viruses that all share characteristics, with SARS-CoV-2 being one of them. When the Corona Virus (referencing SARS-CoV-2) infects our body, we can feel anything from mild to moderate symptoms such as headache, loss of taste or smell, cough, sore throat or breathing difficulties. Viruses contain antigens (viral proteins) on their surfaces which allow specific antibodies to attach to the virus, a process involved in your immunity. They also contain RNA (a single stranded molecule similar to DNA) allowing the virus to replicate in our cells. These specific points will be handy in understanding how the testing processes work.


The Rapid Antigen Test

When you are actively infected with Covid-19, the Corona Virus, as well as it’s antigens will be present within your cells. This method of testing revolves around the detection of these antigens specifically in samples collected from your upper throat or saliva. After collecting your sample using a swab and mixing it with the provided solution, you are instructed to apply the solution to the testing surface. On the testing surface you’ll see the two letters, C and T. In-line with the letter T will be synthetically produced antibodies that have a complimentary fit with Corona Virus antigens. When these antigens are detected in your solution, antibodies bind to them resulting with the production of a red strip at T, thus showing a positive test. For the test to be valid, a red strip must also be present at the letter C, acting as a control. Rapid Antigen tests take only minutes to present results and can be performed in a home setting with minimal equipment, making them an easily accessible and cheap option for the public.


The PCR test

Polymerase Chain Reaction (PCR) tests, a type of Nucleic Acid Amplification Test (NAAT), require a laboratory setting due to the complexity and sensitivity of the testing process. PCR tests are not the only form of molecular/laboratory testing, although it is the most widely used test currently. This type of testing revolves around the detection of corona virus’ genetic material, being the RNA previously mentioned. The swab sample is also taken from the upper throat and saliva, as the pathogen is most likely to replicate in these areas. The sample must then be delivered to a lab.


RNA is a relatively small molecule making it harder to detect in smaller quantities. To overcome this, the RNA is copied multiple times in what’s described as the amplification process. With the RNA copied over and over, its quantity increases and thus becomes easier to detect. The process begins with what scientists call ‘Primers’, molecules which target specific sections of RNA unique to the corona virus that are to be copied. A machine called a ‘Thermocycler’ is then used to promote copying through the control of temperature. The final solution is analysed under a PCR machine, which reads the RNA as fluorescence (light). If there is light emitted, the presence of Corona Virus RNA is confirmed, resulting in a positive test.