Serological testing for SARS-CoV-2 antibodies in clinical practice: a
comparative diagnostic accuracy study
Background: Serological tests are a powerful tool in the
monitoring of infectious diseases and the detection of host immunity.
However, manufacturers often provide diagnostic accuracy data generated
through biased studies and the performance in clinical practice is
essentially unclear. Objectives: We aimed to determine the
diagnostic accuracy of various serological testing strategies for (a)
identification of patients with previous coronavirus disease-2019
(COVID-19) and (b) prediction of neutralizing antibodies against
SARS-CoV-2 in real-life clinical settings. Methods: We
prospectively included 2’573 consecutive health-care workers and 1’085
inpatients with suspected or possible previous COVID-19 at a Swiss
University Hospital. Various serological immunoassays based on different
analytical techniques (enzyme-linked immunosorbent assays, ELISA;
chemiluminescence immunoassay, CLIA; electrochemiluminescence
immunoassay, ECLIA; lateral-flow immunoassay, LFI), epitopes of
SARS-CoV-2 (nucleocapsid, N; receptor-binding domain, RBD; extended RBD,
RBD+; S1 or S2 domain of the spike [S] protein, S1/S2), and antibody
subtypes (IgG, pan-Ig) were conducted. A positive real-time PCR test
from a nasopharyngeal swab was defined as previous COVID-19.
Neutralization assays with live SARS-CoV-2 were performed in a subgroup
of patients to assess neutralization activity (n=201).
Results: The sensitivity to detect patients with previous
COVID-19 was ≥85% in anti-N ECLIA (86.8%) and anti-S1 ELISA (86.2%).
Sensitivity was 84.7% in anti-S1/S2 CLIA, 84.0% in anti-RBD+ LFI,
81.0% in anti-N CLIA, 79.2% in anti-RBD ELISA, and 65.6% in anti-N
ELISA. The specificity was 98.4% in anti-N ECLIA, 98.3% in anti-N
CLIA, 98.2% in anti-S1 ELISA, 97.7% in anti-N ELISA, 97.6% in
anti-S1/S2 CLIA, 97.2% in anti-RBD ELISA, and 96.1% in anti-RBD+ LFI.
The sensitivity to detect neutralizing antibodies was ≥85% in anti-S1
ELISA (92.7%), anti-N ECLIA (91.7%), anti-S1/S2 CLIA (90.3%),
anti-RBD+ LFI (87.9%), and anti-RBD ELISA (85.8%). Sensitivity was
84.1% in anti-N CLIA, and 66.2% in anti-N ELISA. The specificity was
≥97% in anti-N CLIA (100%), anti-S1/S2 CLIA (97.7%), and anti-RBD+
LFI (97.9%). Specificity was 95.9% in anti-RBD ELISA, 93.0% in anti-N
ECLIA, 92% in anti-S1 ELISA, and 65.3% in anti-N ELISA. Diagnostic
accuracy measures were consistent among subgroups.
Conclusions: The diagnostic accuracy of serological tests for
SARS-CoV-2 antibodies varied remarkably in clinical practice, and the
sensitivity to identify patients with previous COVID-19 deviated
substantially from the manufacturer’s specifications. The data presented
here should be considered when using such tests to estimate the
infection burden within a specific population and determine the
likelihood of protection against re-infection.