ABSTRACT
Background. Coronavirus disease 2019 (COVID-19) convalescent plasma (CCP) received an Emergency Use Authorization by the US Food and Drug Administration (FDA). CCP with a signal-to-cutoff ratio of >= 12 using the Ortho VITROS severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunoglobulin G (IgG) test (OVSARS2IgG) is permitted to be labeled "high titer." Little is known about the relationship between OVSARS2IgG ratio and neutralizing capacity of plasma/sera against genuine SARS-CoV-2. Methods. Nine hundred eighty-one samples from 196 repeat CCP donors 0-119 days post-initial donation (DPID) were analyzed. Neutralizing capacity was assessed for 50% (PRNT50) and 90% (PRNT90) reduction of infectious virus using the gold standard plaque reduction neutralization test (PRNT). A subset of 91 donations was evaluated by OVSARS2IgG and compared to PRNT titers for diagnostic accuracy. Results. Of donations, 32.7%/79.5% (PRNT90/PRNT50) met a 1:80 titer initially but only 14.0%/48.8% (PRNT90/PRNT50) met this cutoff >= 85 DPID. Correlation of OVSARS2IgG results to neutralizing capacity allowed extrapolation to CCP therapy results. CCP with OVSARS2IgG ratios equivalent to a therapeutically beneficial group had neutralizing titers of >= 1:640 (PRNT50) and/or >= 1:80 (PRNT90). Specificity and positive predictive value of the OVSARS2IgG for qualifying highly neutralizing CCP was optimal using ratios significantly greater than the FDA cutoff. Conclusions. This information provides a basis for refining the recommended properties of CCP used to treat COVID-19.