Background and objectives: There is a need for conversion of SARS-CoV-2 serology data from different laboratories to a harmonized international unit. We aimed to compare the performance of multiple SARS-CoV-2 antibody serology assays among 25 laboratories across 12 European countries.
Materials and methods: To investigate this we have distributed to all participating laboratories a panel of 15 SARS-CoV-2 plasma samples and a single batch of pooled plasma calibrated to the WHO IS 20/136 standard.
Results: All assays showed excellent discrimination between SARS-CoV-2 seronegative plasma samples and pre-vaccinated seropositive plasma samples but differed substantially in raw antibody titres. Titres could be harmonized to binding antibody units per millilitre by calibration in relation to a reference reagent.
Conclusion: The standardization of antibody quantification is of paramount importance to allow interpretation and comparison of serology data reported in clinical trials in order to identify donor cohorts from whom the most effective convalescent plasma can be collected.
Keywords: COVID-19; convalescent; conversion factor; harmonization; quality control.
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