Abstract
COVID19 convalescent patient plasma units with high titer neutralizing antibody can be used to treat patients with severe disease. Therefore, in order to select suitable donors, neutralizing antibody titer against SARS CoV-2 needs to be determined. Because the neutralization assay is highly demanding from several points of view, a pre-selection of sera would be desirable to minimize the number of sera to be tested. In this study, a total of 140 serum samples that had been titrated for SARS-CoV-2 neutralizing antibody by microneutralization assay were also tested for the presence of anti-SARS-CoV2 antibody using 5 different tests: Architect® immunoassay (Abbott Diagnostics), detecting IgG against the nucleocapsid protein, LIAISON XL® (Diasorin) detecting IgG against a recombinant form of the S1/S2 subunits of the spike protein, VITROS® (Ortho Clinical Diagnostics), detecting IgG against a recombinant form of the spike protein, and ELISA (Euroimmun AG), detecting IgA or IgG against a recombinant form of the S1 subunit. To determine which immunoassay had the highest chance to detect sera with neutralizing antibodies above a certain threshold, we compared the results obtained from the five immunoassays with the titers obtained by microneutralization assay by linear regression analysis and by using receiver operating characteristic curve and Youden's index. Our results indicate that the most suitable method to predict sera with high Nab titer is Euroimmun® IgG, followed closely by Ortho VITROS® Anti-SARS-CoV-2 IgG.