SARS-COV-2 antibodies in patients candidates as donors of immune plasma

Background: In this study SARS-CoV-2 serology was investigated, using three different methods, in a cohort of convalescent patients from SARS-CoV-2 infection, recruited for the establishment of a hyperimmune plasma bank. Methods: SARS-CoV-2 serology was investigated in 326 subjects using three commercial methods: MAGLUMI (MAG) 2019-nCoV IgM CLIA, MAGLUMI 2019-nCoV IgG CLIA and DiaSorin (SOR) LIAISON SARS-CoV-2 S1/S2 IgG. Moreover, 143 subjects were tested using a plaque reduction micro neutralization assay. Results: MAG IgG test and SOR IgG test showed a good agreement (Cohen's K index = 0.65, CI 95% 0.55 - 0.78). Considering SOR IgG test versus micro neutralization test, the observed cut-off values were: 85 AU/mL for a neutralizing titer of 1/80;108 AU/mL for 1/160 titer and 144 AU/mL for 1/320 titer. Considering MAG IgG test versus micro neutralization test, the observed cut-off values were: 4 AU/mL for a neutralizing titer of 1/80, 5 AU/mL for 1/160 titer and 7 AU/mL for 1/320 titer. Conclusions: In our experience, the MAG and SOR tests showed good agreement in identifying subjects with IgG antibodies to SARS-CoV-2. Obtained results confirmed a good correlation between the antibody concentration detected by the SOR IgG and the neutralizing titer determined by the plaque reduction test.