Testing for COVID-19

Types of COVID-19 tests

There are 2 types of COVID-19 tests:

  • PCR (polymerase chain reaction) or molecular tests.
  • Serological tests or antibody tests.

What is a COVID-19 PCR or molecular test?

A PCR test detects the virus in a sample.

It looks for the DNA/RNA or molecular presence of a virus in the sample.  Molecular material is evidence of the virus in the body you currently have the virus. This means an active infection.  It also means that you can infect other people with the virus.

If someone is currently infected with the virus, you can treat and isolate them to prevent the disease from spreading. PCR tests are therefore used to diagnose a COVID-19 infection.  Even if someone is asymptomatic, not showing signs such as fever or cough but has the virus, they will test positive on a PCR test.

PCR tests use swabs from the nose and throat to test.

What is a COVID-19 serological or antibody test?

Serology testing reveals if you were exposed to the virus (infected) and if your body developed antibodies against the virus.

IgM antibodies are present early in infection and IgG antibodies (seroconversion) arise a few days later.  COVID-19 is new for humanity and you will not have COVID-19 antibodies except if you were infected.

The antibody IgM is the bodies first response to an infection.  It normally develops within 5-10 days of an infection taking hold, peaking at 21 days after the infection.  IgG shows that someone has had the virus and is potentially now protected from the virus.  IgG shows up in your blood about 10-14 days after the infection.

Thus, if a patient has IgM antibodies, that suggests they are within the first week of an infection.  If they have both IgM antibodies and IgG antibodies, that suggests they are within the first month of infection.

Serological tests tell you who’s been infected and who should be immune to the virus.  It cannot diagnose a current infection.  We don’t know yet if COVID-19 antibodies will protect you against re-infection.  We also don’t know how long they will last in your blood.  It is to new and we need more conclusive evidence.

Antibody tests use blood samples.  This is because there is a very small amount of the coronavirus circulating in the blood compared to the respiratory tract, but a significant and measurable antibody presence in the blood.

Can a COVID-19 antibody test be performed at home?

No.  There is no at-home, sensitive, disposable test for COVID-19.  COVID-19 antibody tests are for professional use only.

Antibody testing is multipurpose.  It can verify that vaccines are working as intended during clinical trials.  It can be used in contact tracing weeks or longer after a suspected infection in an individual.  It can help public policy makers determine how many people were infected by the coronavirus as it will pick-up the many asymptomatic cases that occurred in a population.  At the moment we are only estimating the total number of people who have been infected.

Keep informed, visit www.sacoronavirus.co.za.