Plasma/serum specimens were analyzed using five commercially available EIAs: the Euroimmun anti-SARS-CoV-2 ELISA, the Epitope Diagnostics, Inc. (EDI), Novel Coronavirus COVID-19 IgG ELISA kit, the ImmunoDiagnostics SARS-CoV-2 NP IgG ELISA kit, the Abbott-Architect SARS-CoV-2 IgG chemiluminescent microparticle immunoassay (CMIA), and the Roche Diagnostics Elecsys anti-SARS-CoV-2 E-CLIA (Table 1 ). These EIAs were selected because data on their performance characteristics in diverse samples are limited, because of the feasibility (with respect to the supply chain) of obtaining the assay kits, and because of the availability of the necessary equipment (e.g., platform). In addition to the inclusion of EIAs that have received an EUA by the FDA for the qualitative detection of SARS-CoV-2 antibodies (Euroimmun, Abbott, Roche), EIAs that have not received an EUA were included as they may still be used for research purposes or may be approved later by the FDA (EDI and ImmunoDiagnostics) (21 (link)). The target antigen for each EIA is the nucleocapsid protein, with the exception of the Euroimmun assay, for which the target antigen is the S1 protein. The Roche assay measures total antibodies to SARS-CoV-2, whereas the others measure only anti-SARS-CoV-2 IgG. Specimens were tested by each EIA based on sample volume availability and assay kit availability at the time of testing. All EIAs were purchased from the manufacturer.
EIAs were conducted according to the manufacturers’ instructions, unless specified otherwise. The intended use of each EIA per the manufacturers’ instructions is the qualitative detection of antibodies; however, each EIA provides continuous output normalized by a calibrator. Indeed, interpretation of the continuous output as a semiquantitative measure is in contradiction with some of the manufacturers’ instructions (i.e., Roche). For simplicity, we refer to the normalized continuous output of each EIA as a “ratio” value. The manufacturers’ cutoff values to indicate positive, indeterminate/borderline, or negative serostatus for SARS-CoV-2 antibodies are listed inTable 1 .
EIAs were conducted according to the manufacturers’ instructions, unless specified otherwise. The intended use of each EIA per the manufacturers’ instructions is the qualitative detection of antibodies; however, each EIA provides continuous output normalized by a calibrator. Indeed, interpretation of the continuous output as a semiquantitative measure is in contradiction with some of the manufacturers’ instructions (i.e., Roche). For simplicity, we refer to the normalized continuous output of each EIA as a “ratio” value. The manufacturers’ cutoff values to indicate positive, indeterminate/borderline, or negative serostatus for SARS-CoV-2 antibodies are listed in
