Journal of Clinical Virology

Volume 138, May 2021, 104797

An evaluation of 4 commercial assays for the detection of SARS-CoV-2 antibodies in a predominantly mildly symptomatic low prevalence Australian population 

Michael C. Wehrhahn, Suzanne J. Brown, James P. Newcombe, Smathi Chong, Jenny Evans, Melanie Figtree, Laurence Hainke, Linda Hueston, Sadid Khan, Elizabeth Marland, Matthew V.N. O’Sullivan, Helen Powell, Jhumur Roy, Lynette Waring, Megan Yu, Jennifer Robson,

Keywords: SARS-CoV-2 IgG; Commercial immunoassay; Neutralising antibody; Immunofluorescent antibody assay

Abstract

A total of 1080 individual patient samples (158 positive serology samples from confirmed, predominantly mildly symptomatic COVID-19 patients and 922 serology negative including 496 collected pre-COVID) from four states in Australia were analysed on four commercial SARS-CoV-2 serological assays targeting antibodies to different antigens (Roche Elecsys and Abbott Architect: nucleocapsid; Diasorin Liaison and Euroimmun: spike). A subset was compared to immunofluorescent antibody (IFA) and micro-neutralisation. Sensitivity and specificity of the Roche (n = 1033), Abbott (n = 806), Diasorin (n = 1034) and Euroimmun (n = 175) were 93.7 %/99.5 %, 90.2 %/99.4 %, 88.6 %/98.6 % and 91.3 %/98.8 %, respectively. ROC analysis with specificity held at 99 % increased the sensitivity for the Roche and Abbott assays from 93.7% to 98.7% (cut-off 0.21) and 90.2 % to 94.0 % (cut-off 0.91), respectively. Overall seropositivity of samples increased from a maximum of 23 % for samples 0−7 days-post-onset of symptoms (dpos), to 61 % from samples 8−14dpos and 93 % from those >14dpos. IFA and microneutralisation values correlated best with assays targeting antibodies to spike protein with values >80 AU/mL on the Diasorin assay associated with neutralising antibody. Detectable antibody was present in 22/23 (96 %), 20/23 (87 %), 15/23 (65 %) and 9/22 (41 %) patients with samples >180dpos on the Roche, Diasorin, Abbott and microneutralisation assays respectively. Given the low prevalence in this community, two-step algorithms on initial positive results saw an increase in the positive predictive value (PPV) of positive samples (39 %–65 % to ≥98 %) for all combinations. Similarly accuracy increased from a range of 98.5 %–99.4 % to ≥99.8 % assuming a 1 % seroprevalence. Negative predictive value (NPV) was high (≥99.8 %) regardless of which assay was used initially.