Abstract
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.