Serologic testing. Antibody Test.
An antibody test tells you who’s been infected and who should be immune to the virus because the antibodies are generated after a week or two, after which time the virus should have been cleared from the system.
Unlike PCR tests, which commonly use swabs to detect Covid-19, blood samples are usually used for antibody tests. This is because there will be a very small amount of the coronavirus circulating in the blood compared to the respiratory tract, but a significant and measurable antibody presence.