The best way to test for COVID-19 is through a PCR test. However, a second kind of test – called an antigen test – provides a faster, relatively affordable and important alternative form of testing in very specific contexts.

In the time of a global pandemic, healthcare authorities across the world try to increase the availability of critical medical products, like the availability of tests to detect whether someone has contracted COVID-19.

Dr Noluthando Nematswerani, head of the Discovery Health Centre for Clinical Excellence said: “This is especially important in the case of a disease like COVID-19 where we have no medicine that directly combats the virus and have not yet vaccinated enough people to provide a degree of protection from illness in the community. Testing is critical in identifying people who have contracted a disease and directing them to self-isolate and focus on their healthcare needs while preventing the spread of infection to others.”

There are two types of Diagnostic Molecular Tests for COVID-19 – they diagnose you while you have an active infection (and so can infect others). These are:

PCR (Polymerase Chain Reaction) tests – the gold standard for testing, as it is the most sensitive (high chance of picking up an infection when it is present in your body) type of test we have access to. Results take from 24 to 48 hours but may be longer in cases where there is widespread community outbreak of infection with high numbers of people requesting testing.

Antigen tests – an important alternative to PCR tests in specific contexts.

So, what are antigen tests, and how do they work?

Antigen tests (also called “rapid diagnostic tests”) detect specific protein on the surface of the virus.

A nasopharyngeal specimen (sample taken from the back of the nose) is taken – in a process carried out by a healthcare professional. Once the sample has been obtained, it is processed using a reagent fluid that breaks up the viral particles and expose the antigens detected by the test. Then, after a short time the sample is applied to the testing strip and a result is obtained. Antigen tests can rapidly and safely detect whether a person has COVID-19.

Dr Nematswerani said: “The fact that antigen tests return a result within 15 to 30 minutes, means that authorities and healthcare workers can quickly triage people and patients and manage them appropriately. Fast identification of people who have COVID-19 allows them to quickly be directed to self-isolate to control the spread of infection.”

There is also a third type of test available – an antibody test – This type of test is not specifically used to diagnose an active COVID-19 infection. However, it is highly effective in identifying people who have already had the infection and may no longer be infectious. This happen if you had an infection without symptoms, which is called an asymptomatic infection.

Antibody tests like the name suggests, test for antibodies not viruses. COVID-19 Antibody tests find the proteins, or antibodies, that our bodies’ immune systems make in response to COVID-19.  The test look to identify two kinds of antibodies that our immune system produces in response to the coronavirus, which are the IgM antibodies and IgG antibodies.

Tests are only for the use of a Registered Health Practitioner (nurse or doctor) and under the correct SAHPRA regulations and requirements. Firstly, cleaning your finger with an alcohol swab, whereafter a new lancet will be used to make a small prick in your finger. With a pipit, a small sample of your blood will be drawn. This sample will then be placed into the circular sample deposit site of the test. Your results will be readily available after a brief 15-30min wait.

When and why we should implement rapid testing?

Testing to be done in confirmed outbreak settings and in the following circumstances:

• Testing symptomatic patients in areas where community spread has been detected.
• Screening and testing of at-risk individuals in the community (elderly, sick).
• Screening and testing of high-risk groups such as healthcare workers and essential staff in areas where community spread has been detected; and
• In the process of contact tracing, to test people who are contacts of both symptomatic and asymptomatic cases.

Did you know?

• Rapid antigen tests are more reliable when they are done on patients who have symptoms of COVID-19 and so likely have a high amount of virus particles in their system – called a high viral load.
• This means that the timing of the test is crucial. Ideally a rapid antigen test should be done within the first five to seven days of the onset of symptoms.

References:

• https://www.discovery.co.za/corporate/covid-19-antigen-testing-available-in-sa
• https://www.cdc.gov/coronavirus/2019-ncov/lab/resources/antigen-tests-guidelines.html
• https://www.who.int/publications/i/item/antigen-detection-in-the-diagnosis-of-sars-cov-2infection-using-rapid-immunoassays
• https://www.ecdc.europa.eu/en/publications-data/options-use-rapid-antigen-tests-covid-19
• https://www.fda.gov/consumers/consumer-updates/coronavirus-disease-2019-testing-basics
• https://www.fda.gov/medical-devices/letters-health-care-providers/potential-false-positive-results-antigen-tests-rapid-detection-sars-cov-2-letter-clinical-laboratory
• https://www.nicd.ac.za/diseases-a-z-index/covid-19/covid-19-guidelines