A Hemagglutination-Based Semiquantitative Test for Point-of-Care Determination of SARS-CoV-2 Antibody Levels.

Serologic point-of-care tests to detect antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are an important tool in the COVID-19 pandemic. The majority of current point-of-care antibody tests developed for SARS-CoV-2 rely on lateral flow assays, but these do not offer quantitative information. To address this, we developed a novel antibody test leveraging hemagglutination, employing a dry card format currently used for typing ABO blood groups. Two hundred COVID-19 patient and 200 control plasma samples were reconstituted with O-negative red blood cells (RBCs) to form whole blood and added to dried viral-antibody fusion protein, followed by a stirring step and a tilting step, 3-min incubation, and a second tilting step. The sensitivities of the hemagglutination test, Euroimmun IgG enzyme-linked immunosorbent assay (ELISA), and receptor binding domain (RBD)-based CoronaChek lateral flow assay were 87.0%, 86.5%, and 84.5%, respectively, using samples obtained from recovered COVID-19 individuals. Testing prepandemic samples, the hemagglutination test had a specificity of 95.5%, compared to 97.3% and 98.9% for the ELISA and CoronaChek, respectively. A distribution of agglutination strengths was observed in COVID-19 convalescent-phase plasma samples, with the highest agglutination score (4) exhibiting significantly higher neutralizing antibody titers than weak positives (2) (P < 0.0001). Strong agglutinations were observed within 1 min of testing, and this shorter assay time also increased specificity to 98.5%. In conclusion, we developed a novel rapid, point-of-care RBC agglutination test for the detection of SARS-CoV-2 antibodies that can yield semiquantitative information on neutralizing antibody titer in patients. The 5-min test may find use in determination of serostatus prior to vaccination, postvaccination surveillance, and travel screening.

A hemagglutination-based, semi-quantitative test for point-of-care determination of SARS-CoV-2 antibody levels.

Serologic, point-of-care tests to detect antibodies against SARS-CoV-2 are an important tool in the COVID-19 pandemic. The majority of current point-of-care antibody tests developed for SARS-CoV-2 rely on lateral flow assays, but these do not offer quantitative information. To address this, we developed a new method of COVID-19 antibody testing employing hemagglutination tested on a dry card, similar to that which is already available for rapid typing of ABO blood groups. A fusion protein linking red blood cells (RBCs) to the receptor-binding domain (RBD) of SARS-CoV-2 spike protein was placed on the card. 200 COVID-19 patient and 200 control plasma samples were reconstituted with O-negative RBCs to form whole blood and added to the dried protein, followed by a stirring step and a tilting step, 3-minute incubation, and a second tilting step. The sensitivity for the hemagglutination test, Euroimmun IgG ELISA test and RBD-based CoronaChek lateral flow assay was 87.0%, 86.5%, and 84.5%, respectively, using samples obtained from recovered COVID-19 individuals. Testing pre-pandemic samples, the hemagglutination test had a specificity of 95.5%, compared to 97.3% and 98.9% for the ELISA and CoronaChek, respectively. A distribution of agglutination strengths was observed in COVID-19 convalescent plasma samples, with the highest agglutination score (4) exhibiting significantly higher neutralizing antibody titers than weak positives (2) (p<0.0001). Strong agglutinations were observed within 1 minute of testing, and this shorter assay time also increased specificity to 98.5%. In conclusion, we developed a novel rapid, point-of-care RBC agglutination test for the detection of SARS-CoV-2 antibodies that can yield semi-quantitative information on neutralizing antibody titer in patients. The five-minute test may find use in determination of serostatus prior to vaccination, post-vaccination surveillance and travel screening.