What Is an Antibody Test? Characteristics of Antibodies against SARS-CoV-2 and Their Tests

Antibodies play a major role in immune responses against viruses, which inhibit infection by binding to target viral antigen. Antibodies are induced by viral entry to the body and vaccination that artificially induces immune responses; therefore, antibody tests are used in research for infection history and evaluation of vaccine efficacy. Currently, antibody tests against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) by immunochromatography, enzyme-linked immunosorbent assay (ELISA), and electrochemiluminescence immunoassay (ECLIA), or other kits used for automated analyzer are available. However, the test results should be carefully interpreted because requirements for the antibody test to obtain reliable results have not been established. Also, antibodies in human samples are heterogeneous, and their expression level changes over time. This review briefly explains the basic knowledge about antibodies against SARS-CoV-2 and outlines the classification and characteristics of the antibody tests with points to consider in their use. A summary of the collaborative study that evaluated the analytical performance of antibody test kits conducted by the National Institute of Health Sciences is also introduced. Then, the issues in ensuring the reliability of antibody tests results are discussed by considering the usefulness and availability of the World Health Organization international standard for anti-SARS-CoV-2 immunoglobulin.