Rapid and Accurate Point-of-care Testing for SARS-CoV2 Antibodies

ABSTRACT The COVID-19 pandemic, caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), has grown into worst public health crisis since the 1918 influenza pandemic. As COVID-19 continues to spread around the world, there is urgent need for a rapid, yet accurate antibody test to identify infected individuals in populations to inform health decisions. We have developed a rapid, accurate and cost-effective serologic test based on antibody-dependent agglutination of antigen-coated latex particles, which uses ∼5 µl plasma and takes <5 min to complete with no instrument required. The simplicity of this test makes it ideal for point-of-care (POC) use at the community level. 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 (N) 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 (ACE2) in a surrogate neutralization assay, suggesting that the agglutination assay may be used to identify individuals with virus-neutralizing antibodies. Intriguingly, we found that >92% of patients had detectable antibodies on the day of positive viral RNA test, suggesting that seroconversion may occur earlier than previously thought and that the agglutination antibody test may complement RNA testing for POC diagnosis of SARS-CoV-2 infection.