The COVID-19 pandemic has now claimed over 2 million deaths worldwide, and this number is only increasing. In response, health agencies have rolled out tests to diagnose and understand the disease. Besides the now widely known PCR test, there is interest in serological (blood) tests that detect “antibodies” against SARS-CoV-2, the virus that causes COVID-19. These blood tests have considerable applications, from identifying blood donors with high levels of anti-SARS-CoV-2 antibodies, whose blood can be used for convalescent plasma therapy, to measuring vaccine effectiveness.