Interim Guidelines for COVID-19 Antibody Testing in Clinical and Public Health Settings [open pdf - 403KB]
From the Background: "Serologic assays for SARS-CoV-2 [severe acute respiratory syndrome coronavirus 2], now broadly available, can play an important role in understanding the virus's epidemiology in the general population and identifying groups at higher risk for infection. Unlike viral direct detection methods such as nucleic acid amplification or antigen detection tests that can detect acutely infected persons, antibody tests help determine whether the individual being tested was ever infected--even if that person never showed symptoms. Serologic tests detect waning or past SARS-CoV-2 virus infection indirectly, by measuring the host humoral immune response to the virus. Therefore, serology assays do not typically replace direct detection methods as the primary tool for diagnosing an active SARS-CoV-2 infection, but they do have several important applications in monitoring and responding to the COVID-19 [coronavirus disease 2019] pandemic."
Centers for Disease Control and Prevention: https://www.cdc.gov/