Related Experiment Video
Updated: Nov 22, 2025
Detection of SARS-CoV-2 Neutralizing Antibodies using High-Throughput Fluorescent Imaging of Pseudovirus Infection
Published on: June 5, 2021
Temporal Analysis of Serial Donations Reveals Decrease in Neutralizing Capacity and Justifies Revised Qualifying
Roxie C Girardin1, Alan P Dupuis1, Anne F Payne1
1Wadsworth Center, New York State Department of Health, Albany, New York, USA.
Insights
COVID-19 convalescent plasma (CCP) high-titer labeling needs better correlation with neutralizing capacity. The Ortho VITROS SARS-CoV-2 IgG test ratio can help identify potent CCP for COVID-19 treatment.
Area of Science:
- Immunology and Virology
- Therapeutic Plasma Development
Background:
- Coronavirus disease 2019 (COVID-19) convalescent plasma (CCP) received Emergency Use Authorization (EUA) from the FDA.
- High-titer CCP is defined by a signal-to-cutoff ratio (≥12) using the Ortho VITROS SARS-CoV-2 IgG test (OVSARS2IgG).
- The relationship between OVSARS2IgG ratio and the neutralizing capacity of CCP against SARS-CoV-2 is not well understood.
Purpose of the Study:
- To investigate the correlation between the OVSARS2IgG ratio and the neutralizing capacity of CCP.
- To determine if the OVSARS2IgG test can accurately identify CCP with high neutralizing titers for COVID-19 treatment.
Main Methods:
- Analyzed 981 samples from 196 repeat CCP donors within 0-119 days post-initial donation (DPID).
- Assessed neutralizing capacity using 50% (PRNT50) and 90% (PRNT90) plaque reduction neutralization tests (PRNT).
- Evaluated a subset of 91 donations using OVSARS2IgG and compared results to PRNT titers for diagnostic accuracy.
Main Results:
- Neutralizing titers decreased over time; only 14.0% (PRNT90) and 48.8% (PRNT50) met initial cutoffs ≥85 DPID.
- CCP with OVSARS2IgG ratios linked to therapeutic benefit showed neutralizing titers of ≥1:640 (PRNT50) and/or ≥1:80 (PRNT90).
- Optimal specificity and positive predictive value for identifying highly neutralizing CCP were achieved with OVSARS2IgG ratios significantly above the FDA cutoff.
Conclusions:
- The OVSARS2IgG test ratio correlates with neutralizing capacity, enabling better characterization of CCP.
- Refining the OVSARS2IgG cutoff can improve the selection of effective CCP for COVID-19 treatment.
Background:
Coronavirus disease 2019 (COVID-19) convalescent plasma (CCP) received an Emergency Use Authorization by the US Food and Drug Administration (FDA). CCP with a signal-to-cutoff ratio of ≥12 using the Ortho VITROS severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunoglobulin G (IgG) test (OVSARS2IgG) is permitted to be labeled "high titer." Little is known about the relationship between OVSARS2IgG ratio and neutralizing capacity of plasma/sera against genuine SARS-CoV-2.
Methods:
Nine hundred eighty-one samples from 196 repeat CCP donors 0-119 days post-initial donation (DPID) were analyzed. Neutralizing capacity was assessed for 50% (PRNT50) and 90% (PRNT90) reduction of infectious virus using the gold standard plaque reduction neutralization test (PRNT). A subset of 91 donations was evaluated by OVSARS2IgG and compared to PRNT titers for diagnostic accuracy.
Results:
Of donations, 32.7%/79.5% (PRNT90/PRNT50) met a 1:80 titer initially but only 14.0%/48.8% (PRNT90/PRNT50) met this cutoff ≥85 DPID. Correlation of OVSARS2IgG results to neutralizing capacity allowed extrapolation to CCP therapy results. CCP with OVSARS2IgG ratios equivalent to a therapeutically beneficial group had neutralizing titers of ≥1:640 (PRNT50) and/or ≥1:80 (PRNT90). Specificity and positive predictive value of the OVSARS2IgG for qualifying highly neutralizing CCP was optimal using ratios significantly greater than the FDA cutoff.
Conclusions:
This information provides a basis for refining the recommended properties of CCP used to treat COVID-19.
