Correlation between SARS-COV-2 antibody screening by immunoassay and neutralizing antibody testing.

ABSTRACT

BACKGROUND: The efficacy of convalescent plasma (CP), an alternative for the treatment of COVID-19, depends on high titers of neutralizing antibodies (nAbs), but 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 CP donors. STUDY DESIGN AND METHODS: A total of 214 CP donors were enrolled and tested for the presence of anti-SARS-CoV-2 antibodies (IgG) using two commercial immunoassays EUROIMMUN (ELISA) and Abbott (Chemiluminescence). Quantification of nAbs was performed using the Cytopathic Effect-based Virus Neutralization test. Three criteria for identifying donors with nAbs ≥ 1160 were tested - C1 Curve ROC; - C2 Conditional decision tree considering only the IA results and - C3 Conditional decision tree including both the IA results and the clinical variables. RESULTS: The performance of the immunoassays was similar referring to both S/CO and predictive value for identifying nAbs titers ≥1160. Regarding the studied criteria for identifying CP donors with high nAbs titers (a) C1 showed 76.1% accuracy if S/CO = 4.65, (b) C2 presented 76.1% accuracy if S/CO ≥4.57 and (c) C3 had 71.6% accuracy if S/CO was ≥4.57 or if S/CO was between 2.68-4.57 and the last COVID-19-related symptoms were recent (within 19 days). CONCLUSION: SARS-CoV-2 IgG immunoassays (S/CO) can be used to predict high anti-SARS-CoV-2 nAbs titers. This study has proposed different criteria for identifying donors with ≥1160 nAbs titers, all with high efficacy.