An Approach to Testing for COVID-19
November 11, 2020

An Approach to Testing for COVID-19

Please follow the guidance of your local health department or Ministry of Health, and reputable organisations like the World Health Organisation and Centres for Disease Control and Prevention. Consult your doctor before acting on information.

COVID-19 or coronavirus disease 2019 is caused by the virus, SARS-CoV-2, which stands for severe acute respiratory syndrome coronavirus-2.

Simply testing for COVID-19 does not tell much about your risk or whether you truly have the virus or have had it and recovered. Talking with your healthcare provider includes talking about your current health status, how likely you were to have been exposed or picked up the virus, any symptoms, deciding the appropriate test to do and interpreting the test results and explaining them to you. A healthcare provider also reminds you of ways to protect yourself and others.

Symptoms

Many persons who become infected may have no symptoms at all. Many will have mild symptoms that look like a common cold or sinusitis. Other symptoms may include cough, shortness of breath, fever, runny nose, joint pains, muscle pains, rash, generalised weakness, diarrhoea or ‘running belly’, loss of sense of taste, or loss of sense of smell.

Structure of the COVID-19 virus

Figure 1. Structure of the virus. The SARS-CoV-2 virus has its genes inside, and is surrounded by protein structures referred to as antigens. Antibodies are made by our bodies to try to fight the virus.

Which test to do and when

In a previous article on the subject, we discussed the considerations that go into accurately testing for a virus. Here, we delve into the 3 main types of tests for COVID-19 which are recommended at different stages of potential infection. These are:

PCR Test:

  • PCR test picks up the genes of the virus.
  • Usually requires a swab of the back of the nose or throat.
  • Because PCR looks for the genes of the virus, it may not tell if genes are from living virus or dead virus.

Antigen Test:

  • Usually requires a swab of the nose.
  • Antigen tests look for parts from the structure of the virus, but not the genes of the virus.
  • This test works best when there is a lot of virus in your airway. When there is a lot of virus in the airway, it is easier for the virus to be passed on to others.
  • Most likely to detect virus about 5 to 7 days since symptoms started; after these 7 days or so, even if you have the virus an antigen test is not likely to detect it.

Antibody Test:

  • Usually a blood test.
  • Your body needs time to make these antibodies, and so they tend to appear later, like 1 to 2 weeks after becoming infected.
  • Can be a finger-prick rapid test or blood is drawn and sent to a lab.
  • When blood is collected into a tube and sent to the lab, the test tends to be more accurate than finger-prick rapid tests.
  • We do not yet know how long these antibodies last or if they are good at protecting against future infection.

Tests for COVID-19

Figure 2. Which test to do and when.

Red line = levels of genes or RNA from the virus in the body after infection;

Blue line = levels of antigen from the virus in the body over time;

Green line = levels of antibodies made by the body over time.

Notice that antibodies come about after the virus has been in the body for some time.

Remember to protect yourself and your loved ones by:

  • washing your hands often,
  • covering your cough or sneeze,
  • staying away from gatherings,
  • staying away from others if you feel ill or have symptoms of a cold or flu,
  • similarly staying away from persons who are ill.

A test is an important tool in finding out if someone has the virus and helping to stop the spread. No test is perfect, and this has to be considered when interpreting their results. Sometimes, it may even be necessary to do another test at another time.

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