Clinical predictors of SARS-CoV-2 neutralizing antibody titers in COVID-19 convalescents: Implications for convalescent plasma donor recruitment.

While COVID-19 convalescent plasma (CCP) efficacy is still under investigation in randomized controlled trials (RCT), CCP collections continue worldwide with largely variable criteria. Since it is well known that only a minority of patients develop high-titer neutralizing antibodies (nAb), as assessed by the viral neutralization tests (VNT), strategies to maximize cost-effectiveness of CCP collection are urgently needed. A growing amount of the population is having exposure to the virus and is hence becoming a candidate CCP donor. Laboratory screening with high-throughput serology has good correlations with the VNT titer, but upstream screening using clinical surrogates would be advisable. We review here the existing literature on clinical predictors of high-titer nAb. Older age, male sex, and hospitalization are the main proxies of high VNT and should drive CCP donor recruitment.