Validation of a commercially available SARS-CoV-2 serological immunoassay

B Meyer; G Torriani; S Yerly; L Mazza; A Calame; I Arm-Vernez; G Zimmer; T Agoritsas; J Stirnemann; H Spechbach; I Guessous; S Stringhini; J Pugin; P Roux-Lombard; L Fontao; C-A Siegrist; I Eckerle; N Vuilleumier; L Kaiser; Geneva Center for Emerging Viral Diseases

doi:10.1016/j.cmi.2020.06.024

Validation of a commercially available SARS-CoV-2 serological immunoassay

Clin Microbiol Infect. 2020 Oct;26(10):1386-1394. doi: 10.1016/j.cmi.2020.06.024. Epub 2020 Jun 27.

Authors

B Meyer¹, G Torriani², S Yerly³, L Mazza³, A Calame⁴, I Arm-Vernez³, G Zimmer⁵, T Agoritsas⁶, J Stirnemann⁷, H Spechbach⁸, I Guessous⁸, S Stringhini⁹, J Pugin¹⁰, P Roux-Lombard¹¹, L Fontao¹², C-A Siegrist¹, I Eckerle¹³, N Vuilleumier¹⁴, L Kaiser¹⁵; Geneva Center for Emerging Viral Diseases

Affiliations

¹ Centre for Vaccinology, Department of Pathology and Immunology, University of Geneva, Geneva, Switzerland.
² Department of Microbiology and Molecular Medicine, University of Geneva, Geneva, Switzerland.
³ Laboratory of Virology, Geneva University Hospitals, Geneva, Switzerland.
⁴ Division of Infectious Disease, Geneva University Hospitals, Geneva, Switzerland.
⁵ Institute of Virology and Immunology (IVI), Mittelhäusern, Switzerland; Department of Infectious Diseases and Pathobiology (DIP), Vetsuisse Faculty, University of Bern, Bern, Switzerland.
⁶ Division of General Internal Medicine, Department of Medicine, Geneva University Hospitals, Geneva, Switzerland; Department of Health Research Methods, Evidence, and Impact, Hamilton, Ontario, Canada.
⁷ Division of General Internal Medicine, Department of Medicine, Geneva University Hospitals, Geneva, Switzerland.
⁸ Division and Department of Primary Care Medicine, Geneva University Hospitals, Geneva, Switzerland.
⁹ Division and Department of Primary Care Medicine, Geneva University Hospitals, Geneva, Switzerland; Unit of Population Epidemiology, Division of Primary Care, Geneva University Hospitals, Geneva, Switzerland.
¹⁰ Division of Intensive Care, Geneva University Hospitals, Geneva, Switzerland.
¹¹ Division of Laboratory Medicine, Department of Diagnostics, Geneva University Hospitals and Geneva University, Geneva, Switzerland.
¹² Division of Dermatology and of Laboratory Medicine, Geneva University Hospitals, Geneva, Switzerland.
¹³ Department of Microbiology and Molecular Medicine, University of Geneva, Geneva, Switzerland; Division of Infectious Disease, Geneva University Hospitals, Geneva, Switzerland; Geneva Centre for Emerging Viral Diseases, Geneva University Hospitals, Geneva, Switzerland.
¹⁴ Division of Laboratory Medicine, Department of Diagnostics, Geneva University Hospitals and Geneva University, Geneva, Switzerland; Division of Laboratory Medicine, Department of Medicine, Faculty of Medicine, Geneva, Switzerland.
¹⁵ Laboratory of Virology, Geneva University Hospitals, Geneva, Switzerland; Division of Infectious Disease, Geneva University Hospitals, Geneva, Switzerland; Geneva Centre for Emerging Viral Diseases, Geneva University Hospitals, Geneva, Switzerland. Electronic address: Laurent.Kaiser@hcuge.ch.

Abstract

Objectives: To validate the diagnostic accuracy of a Euroimmun SARS-CoV-2 IgG and IgA immunoassay for COVID-19.

Methods: In this unmatched (1:2) case-control validation study, we used sera of 181 laboratory-confirmed SARS-CoV-2 cases and 326 controls collected before SARS-CoV-2 emergence. Diagnostic accuracy of the immunoassay was assessed against a whole spike protein-based recombinant immunofluorescence assay (rIFA) by receiver operating characteristic (ROC) analyses. Discrepant cases between ELISA and rIFA were further tested by pseudo-neutralization assay.

Results: COVID-19 patients were more likely to be male and older than controls, and 50.3% were hospitalized. ROC curve analyses indicated that IgG and IgA had high diagnostic accuracies with AUCs of 0.990 (95% Confidence Interval [95%CI]: 0.983-0.996) and 0.978 (95%CI: 0.967-0.989), respectively. IgG assays outperformed IgA assays (p=0.01). Taking an assessed 15% inter-assay imprecision into account, an optimized IgG ratio cut-off > 2.5 displayed a 100% specificity (95%CI: 99-100) and a 100% positive predictive value (95%CI: 96-100). A 0.8 cut-off displayed a 94% sensitivity (95%CI: 88-97) and a 97% negative predictive value (95%CI: 95-99). Substituting the upper threshold for the manufacturer's, improved assay performance, leaving 8.9% of IgG ratios indeterminate between 0.8-2.5.

Conclusions: The Euroimmun assay displays a nearly optimal diagnostic accuracy using IgG against SARS-CoV-2 in patient samples, with no obvious gains from IgA serology. The optimized cut-offs are fit for rule-in and rule-out purposes, allowing determination of whether individuals in our study population have been exposed to SARS-CoV-2 or not. IgG serology should however not be considered as a surrogate of protection at this stage.

Keywords: COVID-19; ELISA; Pseudovirus neutralisation assay; Recombinant immunofluorescence assay; SARS-CoV-2; Serological assays; Serological testing strategy.

Publication types

Validation Study

MeSH terms

Adult
Antibodies, Viral / blood*
Area Under Curve
Betacoronavirus / immunology*
COVID-19
COVID-19 Testing
Case-Control Studies
Child
Clinical Laboratory Techniques / methods*
Coronavirus Infections / diagnosis*
Coronavirus Infections / immunology
Coronavirus Infections / physiopathology
Coronavirus Infections / virology
Female
Humans
Immune Sera / chemistry
Immunoassay / standards*
Immunoglobulin A / blood*
Immunoglobulin G / blood*
Male
Pandemics
Pneumonia, Viral / diagnosis*
Pneumonia, Viral / immunology
Pneumonia, Viral / physiopathology
Pneumonia, Viral / virology
ROC Curve
SARS-CoV-2
Sensitivity and Specificity
Severity of Illness Index

Substances

Antibodies, Viral
Immune Sera
Immunoglobulin A
Immunoglobulin G