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. 2022 Jan 19;60(1):e0174621.
doi: 10.1128/JCM.01746-21. Epub 2021 Oct 27.

Evaluation of Commercial Anti-SARS-CoV-2 Antibody Assays and Comparison of Standardized Titers in Vaccinated Health Care Workers

Kahina Saker  1 , Vanessa Escuret  1   2 , Virginie Pitiot  3 , Amélie Massardier-Pilonchéry  3 , Stéphane Paul  4 , Bouchra Mokdad  1 , Carole Langlois-Jacques  5 , Muriel Rabilloud  5 , David Goncalves  6 , Nicole Fabien  6 , Nicolas Guibert  3 , Jean-Baptiste Fassier  3 , Antonin Bal  1   2 , Sophie Trouillet-Assant  1   2 , Mary-Anne Trabaud  1
Affiliations

Evaluation of Commercial Anti-SARS-CoV-2 Antibody Assays and Comparison of Standardized Titers in Vaccinated Health Care Workers

Kahina Saker et al. J Clin Microbiol. .

Abstract

With the availability of vaccines, commercial assays detecting anti-severe acute respiratory syndrome coronavirus-2 antibodies (Ab) evolved toward quantitative assays directed to the spike glycoprotein or its receptor binding domain (RBD). The main objective of the present study was to compare the Ab titers obtained with quantitative commercial binding Ab assays, after one dose (convalescent individuals) or two doses (naive individuals) of vaccine, in health care workers (HCW). Antibody titers were measured in 255 sera (from 150 HCW) with five quantitative immunoassays (Abbott RBD IgG II quant, bioMérieux RBD IgG, DiaSorin Trimeric spike IgG, Siemens Healthineers RBD IgG, Wantai RBD IgG). One qualitative total antibody anti-RBD detection assay (Wantai) was used to detect previous infection before vaccination. The results are presented in binding Ab units (BAU)/mL after application, when possible, of a conversion factor provided by the manufacturers and established from a World Health Organization internal standard. There was a 100% seroconversion with all assays evaluated after two doses of vaccine. With assays allowing BAU/mL correction, Ab titers were correlated (Pearson correlation coefficient, ρ, range: 0.85-0.94). The titer differences varied by a mean of 10.6% between Siemens and bioMérieux assays to 60.9% between Abbott and DiaSorin assays. These results underline the importance of BAU conversion for the comparison of Ab titer obtained with the different quantitative assays. However, significant differences persist, notably, between kits detecting Ab against the different antigens. A true standardization of the assays would be to include the International Standard in the calibration of each assay to express the results in IU/mL.

Keywords: SARS-CoV-2 antibodies; commercial assays; health care workers; immunization; quantification; standardized titers; vaccination.

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Figures

FIG 1
FIG 1
Comparison of anti-SARS-CoV-2 antibodies concentration (BAU/mL) between all assays in sera collected from vaccinated subjects. The statistical difference was evaluated by Wilcoxon’s test. Comparison of median titers between Siemens, DiaSorin, bioMérieux, and Abbott assays. BAU/mL, binding antibodies unit/mL; ****, P < 0.0001. Data from patients scheduled to be vaccinated with two doses of Pfizer BioNtech vaccine (black) or with one dose of AstraZeneca vaccine followed by one dose of Pfizer BioNtech (blue) are presented.
FIG 2
FIG 2
Passing and Bablok regression analyses using the Siemens, DiaSorin, bioMérieux, and Abbott assays. (A) The Siemens assay compared with the DiaSorin assay. (B) bioMérieux compared with DiaSorin. (C) Abbott compared with DiaSorin. (D) Siemens compared with bioMérieux. (E) Siemens compared with Abbott. (F) Abbott compared with bioMérieux.
FIG 3
FIG 3
Bland-Altman plots comparing agreement between concentrations determined using the Siemens, DiaSorin, bioMérieux, and Abbott assays. (A) The Siemens assay compared with the DiaSorin assay. (B) bioMérieux compared with DiaSorin. (C) Abbott compared with DiaSorin. (D) Siemens compared with bioMérieux. (E) Siemens compared with Abbott. (F) Abbott compared with bioMérieux. The solid blue line represents the bias between assays, the dashed blue lines represent 95% CI.
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