Rapid and accurate agglutination-based testing for SARS-CoV-2 antibodies

Abstract

Summary: We have developed a rapid, accurate, and cost-effective serologic test for SARS-CoV-2 virus, which caused the COVID-19 pandemic, on the basis of antibody-dependent agglutination of antigen-coated latex particles. When validated using plasma samples that are positive or negative for SARS-CoV-2, the agglutination assay detected antibodies against the receptor-binding domain of the spike (S-RBD) or the nucleocapsid protein of SARS-CoV-2 with 100% specificity and ∼98% sensitivity. Furthermore, we found that the strength of the S-RBD antibody response measured by the agglutination assay correlated with the efficiency of the plasma in blocking RBD binding to the angiotensin-converting enzyme 2 in a surrogate neutralization assay, suggesting that the agglutination assay might be used to identify individuals with virus-neutralizing antibodies. Intriguingly, we found that >92% of patients had detectable antibodies on the day of a positive viral RNA test, suggesting that the agglutination antibody test might complement RNA testing for the diagnosis of SARS-CoV-2 infection. Motivation: As COVID-19 continues to spread around the world, there is urgent need for a rapid yet accurate antibody test to detect individuals' humoral immune responses to the SARS-CoV-2 virus and emerging variants of concern. A simple and reliable antibody test would also allow longitudinal analysis of antibody responses to inform vaccination strategies. We addressed this pressing need by developing a simple, quick, and sensitive antibody test based on latex particle agglutination.

Keywords

• SARS-CoV-2
• COVID-19
• antibody test
• serology
• agglutination assay
• rapid testing