Put simply, a COVID-19 antibody blood test can be used to detect antibodies in your blood. Antibodies are part of the body's immune system and are created to defend the body when it detects potentially harmful infections (known as pathogens).
This is a companion discussion topic for the original article at https://patient.info/news-and-features/what-is-the-covid-19-vaccine-response-antibody-blood-test