ABSTRACT
Background. Serologic assays detecting antibodies against the SARS-CoV-2 spike or nucleocapsid proteins have been developed to advance our understanding of the prognosis and clinical course of the COVID-19 disease. We recently developed a red cell agglutination-based assay to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies. This assay uses peptide fragments of the SARS-CoV-2 spike protein to label red cells (C19-kodecytes). We performed a clinical evaluation of this C19-kodecyte assay in COVID-19 convalescent plasma (CCP) donors previously assessed with 2 commercial immunoassays and a virus neutralizing assay. Methods. Red cells were coated with peptide fragments of the SARS-CoV-2 spike protein. We tested plasma samples from 140 CCP donors. The results were compared with those of a virus neutralizing assay and 2 commercial chemiluminescent antibody tests: anti-SARS-CoV-2 Total (IgG, IgM and IgA) assay and anti-SARS-CoV-2 IgG assay (Ortho). Inter-rater agreement between the different assays was measured using Cohen's kappa. Specificity was tested with 150 plasma samples, collected in 2008, more than a decade before the COVID-19 outbreak and with 125 plasma samples, collected in 2020 from consecutive healthy volunteer donors, who tested negative for the Ortho Total assay. Testing was performed using the column agglutination technique commonly employed for blood typing. Results. The area under the ROC curve (AUC) for the C19-kodecyte assay reached 0.95 (95% CI: 0.93 - 0.97) with sensitivity of 92.8% (95% CI: 86.9% - 96.3%) and specificity of 96.3% (95% CI: 93.2% - 98.1%). In almost all of the 40 CCP donors with longitudinal data, the antibody concentration decreased during the follow-up, which ranged from 7 to 44 weeks. In the 140 CCP donors, we compared the C19-kodecyte score to the antibody concentrations from the 2 FDA authorized assays (Ortho Total and Ortho IgG) and the titer in the neutralizing assay. There was a positive relationship between the results of all 4 assays. The Spearman's correlation of our assay was 0.20 with the neutralizing assay (0.49 with IgG, and 0.41 with Total assays). Conclusions. Sensitivity and specificity of the C19-kodecyte assay were within the minimum performance range required by the FDA for EUA authorization of serology tests. The limited correlation in assay reaction strengths suggested that the assays may be influenced by different antibody specificities. Unlike the other 84 FDA authorized serologic tests for SARS-CoV-2, this C19-kodecyte assay is a simple and rapid test that can be easily established in any blood typing laboratory worldwide using its routine setup for column agglutination or tube technique. The technique could vastly improve assay capacity, particularly in resource limited hospital blood banks. Disclosures: Bovin: Kode Biotech: Current Employment, Current holder of stock options in a privately-held company. Henry: Kode Biotech: Current Employment, Current holder of stock options in a privately-held company.
ABSTRACT
Background/Case Studies: We had developed a simple and rapid red cell agglutination assay for serologic screening of antibodies to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We evaluated this new C19-kodecyte assay in a cohort of convalescent patients with PCR-confirmed SARS-CoV-2 infection and compared its analytical performance with three established assays. Study Design/Methods: Red cells modified with peptides from SARS-CoV-2 spike protein using the Kode Technology were prepared.We tested plasma samples from 140 convalescent plasma donors and 125 healthy donors that had tested negative for anti-SARS-CoV-2 Total (Ortho). Plasma samples were stored at -30 °C before testing. Testing was performed using the column agglutination technology commonly employed for blood typing. The results were evaluated and compared with the results of a virus neutralization assay and two commercial chemiluminescent antibody tests: Ortho anti-SARS-CoV-2 Total (IgG, IgM and IgA) assay and Ortho anti-SARS-CoV-2 IgG antibody assay. Results/Findings: The median time interval from the onset of symptoms and plasma donation was 94 days (range: 33 - 331 days). Our simple and rapid C19-kodecyte assay detected SARS-CoV-2 antibodies with a specificity of 95.2% and sensitivity of 92.1%. Correlation analysis of measurement data among the different platforms showed a weak to moderate concordance. The Pearson correlation coefficient ranged between 0.21 and 0.28 for C19-kodecyte versus Ortho anti-SARS-CoV-2 Total and Ortho anti-SARS-CoV-2 IgG assays while it was 0.24 between C19-kodecyte and neutralizing titer. Agreements among C19-kodecyte versus Ortho anti-SARS-CoV-2 Total and Ortho anti-SARS-CoV-2 IgG assays were moderate: 0.41 (0.09-0.73) and 0.41 (0.14-0.68), respectively. Conclusions: Sensitivity and specificity of the C19-kodecyte assay are within the estimated range of FDA issued EUA authorized serology tests (88% to 100% sensitivity and 95% to 100% specificity). The low correlation between C19-kodecyte versus Ortho anti-SARSCoV- 2 results and between C19-kodecyte versus neutralizing titer suggests that COVID-19 patients develop a broad antibody repertoire against multiple SARS-CoV-2 proteins and epitopes and different assays detect diverse antibody specificities. Our easily scalable approach using C19-kodecytes can be operated in blood typing laboratories worldwide using common routine setups. The availability of standard blood group serology techniques for SARS-CoV-2 antibody screening could vastly improve assay capacity. This would be particularly useful in developing countries, where dedicated virology and microbiology may be lacking the necessary turnaround capacity.