What is a rapid antigen test?

The gold standard test for SARS-CoV-2 is called a reverse transcription polymerase chain reaction (RT-PCR) test. This test involves looking for the RNA of the virus through a nasopharyngeal swab sample.

PCR tests are very accurate. So much so that they can find tiny traces of viral RNA that may only lead to harmless asymptomatic infections, or even provide a positive diagnosis weeks after a person has passed the infectious period.

But PCR testing is also time- and energy-intensive, requiring samples to be sent to a diagnostic laboratory. In the best-case scenario, the results of a PCR test can take several hours. And in the worst-case scenario, when the lab is overwhelmed, it may take days before results are available.

On the other hand, rapid COVID-19 assays sacrifice a degree of accuracy for speed and simplicity.

These assays look for proteins on the surface of the virus, called antigens or antibody generators.

Rapid tests contain a set of antibodies designed to react to the SARS-CoV-2 antigen, and they can return a positive or negative result in about 15 minutes.

How accurate are they?

There is no doubt that rapid antigen tests are not as accurate as PCR tests. However, rapid antigen tests are incredibly accurate at capturing the strongest infections in a case. Rapid tests require a large amount of virus to be present in any given swab. This means that these tests do not confirm that someone is not currently infected with SAR-CoV-2, but rather can confirm if a person is infectious at the time of testing.