CORRELATION BETWEEN SARS-COV-2 ANTIBODY SCREENING BY IMMUNOASSAY AND NEUTRALIZING ANTIBODY TESTING

Background: Passive antibody therapy with convalescent plasma (CP) represents a promising alternative for the treatment of SARS CoV 2 infection. The efficacy of CP therapy has been associated with high titers of neutralizing antibodies (nAbs) in the plasma of recovered patients, but the assays for quantifying nAbs are not widely available. Our goal was to develop a strategy to predict high titers of nAbs based on the results of anti-SARS CoV 2 immunoassays and the clinical characteristics of the CP potential donors. Methods: Two hundred and fourteen CP donors were enrolled and tested for the presence of anti-SARS CoV 2 antibodies using two commercial immunoassays (IA): Anti SARS CoV 2 ELISA IgG EUROIMMUN and Anti SARS CoV 2 Chemiluminescence IgG Abbott. In parallel, quantification of neutralizing antibodies (nAbs) was performed using the Cytopathic effect-based virus neutralization test (CPE VNT). Three criteria for identifying donors with high titers of nAbs (more than 160) were tested: Criterion1: Curve ROC Method; Criterion 2: Conditional decision tree considering only the results from the IA and Criterion 3: Conditional decision tree including both the IA results and the clinical variables. Results: The performance of Abbott and EUROIMMUN immunoassays was similar referring to both S/CO and predictive value for identifying nAbs titers more than 1:160. Regarding the three studied criteria for identifying CP donors with high nAbs titers (more than 1:160): 1) Criterion 1 showed 76.1% accuracy when the S/CO cut-off of 4.65 was used, 2) Criterion 2 presented 76.1% accuracy if the S/CO more than 4.57 was applied and 3) Criterion 3 had 71.6% accuracy if either S/CO more than 4.57 or S/CO between 2.68 and 4.57 and the last COVID-19-related symptoms occurred less than 19 days from donor recruiting were used. Conclusion: The results of SARS-CoV-2 immunoassays (S/CO) can be used to predict high nAbs titers of potential CP donors. This study has proposed three different criteria for identifying donors with more than 160 nAbs titer based on either solely S/CO results or S/CO together with clinical variables, all with high efficacy and accuracy.