Video explains how antibody testing works. Part 2 in a 4-part series on serologic testing. A serologic test, also known as antibody test, looks for antibodies to viruses in the blood stream. Antibodies are disease-specific proteins that help fight off infections, and their presence in your blood can help determine whether you have been exposed to and infected with the SARS-CoV-2 virus, which causes COVID-19 disease.