COVID-19 Antibody Detection and Assay Performance Using Red Cell Agglutination.

Red cells can be labeled with peptides from the SARS-CoV-2 spike protein (C-19 kodecytes) and used as reagent cells for serologic screening of SARS-CoV-2 antibodies. We evaluated 140 convalescent COVID-19 donors and 275 healthy controls using C19-kodecytes. The analytical performance of the C19-kodecyte assay was compared with a virus neutralizing assay and two commercial chemiluminescent antibody tests (Total assay and IgG assay, Ortho). The C19-kodecyte assay detected SARS-CoV-2 antibodies with a sensitivity of 92.8% and specificity of 96.3%, well within the minimum performance range required by FDA for EUA authorization of serologic tests. The Cohen's kappa coefficient was 0.90 indicating an almost perfect agreement with the Total assay. The Spearman's correlation coefficient was 0.20 with the neutralizing assay (0.49 with IgG, and 0.41 with Total assays). The limited correlation in assay reaction strengths suggested that the assays may be influenced by different antibody specificities. The C19-kodecyte assay is easily scalable and may vastly improve test capacity in any blood typing laboratory using its routine column agglutination platforms. IMPORTANCE We recently developed a red cell based assay to detect SARS-CoV-2 antibodies in human plasma. In the current study, we show the hands-on application of this assay in a group of COVID-19 convalescent plasma donors and healthy individuals. We compared our assay against three published assays, including two that are widely used for patient care in the United States. Our assay compared well with all three assays. Our easily scalable assay can be used for population-wide screening of SARS-CoV-2 antibody status. It can be readily established in any hospital blood bank worldwide using its routine equipment.