Study design
The study was approved by the local ethics committee (BC-07829) of the Ghent University Hospital, a 1062-beds tertiary care teaching hospital in Belgium. From March 12th to 31st 2020, 23 consecutive sera from 7 different patients, admitted to the hospital with a confirmed diagnosis of COVID-19 based on positive RT-PCR [6], were collected on day 2 to 18 after symptom onset. The study group consisted of 2 females and 5 males. The median age was 58 years (range 39–81 years). The collected sera were divided into 2 groups: day 2–7 after symptom onset (7 samples) and day 8–18 after symptom onset (16 samples) in order to evaluate clinical sensitivity.
Specificity was evaluated using 10 pre-pandemic sera, i.e. clinical samples sent to the hospital laboratory for non-COVID-19-related serological investigations from August to September 2019. Furthermore, 9 potential cross-reactive sera were included, i.e. IgM positivity against Cytomegalovirus (CMV) (n = 2), Epstein-Barr virus (EBV) (n = 2) or Toxoplasma gondii (Toxo) (n = 1); samples positive for rheumafactor (RF) (n = 1) or anti-nuclear factor (ANF) (n = 1)) and sera from patients positive for non-SARS-CoV-2 endemic coronaviruses (OC43 and NL63) (n = 2).
The 14 serological assays listed in Table 1 were performed on each of the 23 sera from PCR confirmed COVID-19 positive patients and the 19 pre-pandemic/cross-reactive sera, according to the manufacturer’s instructions. Sensitivity and specificity were calculated for each test. We calculated both the overall sensitivity (day 2–18 after symptom onset) and the sensitivity of the two subgroups (day 2–7 and day 8–18), each time for IgM/A and IgG separately and for combined IgM/A and IgG testing.
Table 1. Overview of the included assays
Test Assay Company Antibody detection Recombinant antigen
Point-of-care test
Corona Virus (COVID-19) Combined IgM/IgG Rapid Test Sol Scientifics IgM+IgG Not specified
COVID-19 IgG/igM Rapid Test Cassette Zhejiang ORIENT GENE Biotech IgM+IgG Spike + nucleocapsid protein
Wantai SARS-COV-2 Ab Rapid Test Beijing Wantai Biological Pharmacy Enterprise IgM+IgG (combined) Not specified
COVID-19 IgG/IgM RAPID TEST PRIMA PROFESSIONAL IgM+IgG Not specified
Diagnostic Kit for IgG/IgM Antibody to SARS-CoV-2 WIZ BIOTECH IgM+IgG Not specified
Enzyme-Linked Immunosorbent Assay (ELISA)
Anti-SARS-CoV-2 ELISA (IgA) EUROIMMUN S1 Spike glycoprotein (S1domain)
Anti-SARS-CoV-2 ELISA (IgG) EUROIMMUN IgG Spike glycoprotein (S1domain)
Novel Coronavirus COVID-19 IgM ELISA Kit Epitope Diagnostics (EDI) IgM Not specified
Novel Coronavirus COVID-19 IgG ELISA Kit Epitope Diagnostics (EDI) IgG Nucleocapsid protein
SARS-CoV-2 IgM ELISA Kit Creative Diagnostics IgM Not specified
SARS-CoV-2 IgG ELISA kit Creative Diagnostics IgG Not specified
Human Anti-2019 nCoV(N) IgG ELISA kit Finetest, Wuhan Fine Biotech Co., Ltd. IgG Spike glycoprotein (S1domain)
Chemiluminescent microparticle immunoassay (CMIA)
SARS-CoV-2 IgG Abbott IgG Nucleocapsid protein
Chemiluminescence immunoassay (CLIA)
Liaison SARS-CoV-2 S1/S2 IgG DiaSorin IgG S1 and S2 protein
Sensitivity and specificity were calculated by means of Excel (version 16.0, Microsoft, Washington, USA) using the following definitions in Excel:
Sensitivity = 100 x [True Positive/(True Positive + False Negative)]
Specificity = 100 x [True Negative/(True Negative +False Positive)]
All patients consulting at the emergency department of our hospital from the 1st of March till the 14th of May, with symptoms suggestive of COVID-19 disease that required hospital admission and for which laboratory diagnosis was performed in our institution were retrospectively included in a database. In all patients a RT-PCR test on nasopharyngeal/throat swab was performed at the time of admission. If the initial nasopharyngeal swab was found to be negative, a second nasopharyngeal and additional anal swab were analyzed. If still negative, a bronchoalveolar lavage (BAL) was performed. Patients with repetitive negative molecular testing for SARS-CoV-2 but high clinical, epidemiological and/or radiological suspicion of COVID-19 disease were subjected to serological testing using COVID-19 IgG/IgM rapid test (Prima Professional®). Among this retrospective cohort of hospitalized patients clinically treated for COVID-19 disease, we calculated the number of patients that ultimately had a RT-PCR confirmed diagnosis. As such, an estimation of the added diagnostic value of SARS-CoV-2 serology in this cohort could be calculated.