The most important use of serology in the COVID-19
diagnostics is for determination of the extent of disease in the population. However, immunoassays could represent an additional diagnostic method,
especially in patients with exposure history and clinical symptoms compatible
with COVID-19 who failed to be confirmed by RT-PCR. We analyzed the preliminary
results of six serology tests for the diagnosis of SARS-CoV-2. Three
point-of-care lateral flow chromatographic immunoassays (POC): ACRO, AMP and
ENCODE and three enzyme immunoassays (ELISA): DiaPro, Vircell and Euroimmun
were used. A total of 15 serum samples from COVID-19 patients and 15 serum
samples from asymptomatic persons were tested. Time of sampling for COVID-19
patients was 4 – 10 days (N=4), 11 – 19 days (N=6) and 20 – 34 days (N=5) after
disease onset. Initially reactive results were confirmed using a virus
neutralization test (VNT). In COVID-19 patients (N=15), IgM/IgA positive
detection rates were 9/60.0% (ACRO), 11/73.3% (AMP, ENCODE, Euroimmun), 12/80.0%
(DiaPro) and 13/86.6% (Vircell). Overall IgG detection rates were 10//66.6%
(AMP, Euroimmun) and 11/73.3% (other tests). According to the sampling time,
positive detection rates were as follows: a) days 4 – 10: 1/25.0% and 2/50.0% (IgM/IgA
and IgG); b) days 11 –19: 4/66.6%-6/100% (IgM/IgA), 4/66.6% and 5/83.3% (IgG);
c) days 20 – 34: 4/80.0% and 5/100% (IgM/IgA), 5/100% (IgG). One asymptomatic
participant tested IgM/IgA positive using ACRO, DiaPro and Vircell was
confirmed seropositive using a VNT. In a group of asymptomatic persons detected
seronegative using a VNT (N=14), IgM/IgA negative detection rates were 12/85.7%
(ACRO), 13/92.8% (DiaPro, Vircell) and 14/100% (AMP, ENCODE, Euroimmun). IgG
negative detection rates were 13/92.8% (ACRO) and 14/100% (other tests). ELISA tests showed a higher overall
IgM/IgA sensitivity compared to POC tests in patients with COVID-19, while the IgG
sensitivity was similar in both POC and ELISA.