Examination of SARS-CoV-2 serological test results from multiple commercial and laboratory platforms with an in-house serum panel

Abstract

Severe acute respiratory syndrome (SARS) coronavirus 2 (SARS-CoV-2) is a novel human coronavirus that was identified in 2019. SARS-CoV-2 infection results in an acute, severe respiratory disease called coronavirus disease 2019 (COVID-19). The emergence and rapid spread of SARS-CoV-2 has led to a global public health crisis, which continues to affect populations across the globe. Real time reverse transcription polymerase chain reaction (rRT-PCR) is the reference standard test for COVID-19 diagnosis. Serological tests are valuable tools for serosurveillance programs and establishing correlates of protection from disease. This study evaluated the performance of one in-house enzyme linked immunosorbent assay (ELISA) utilizing the pre-fusion stabilized ectodomain of SARS-CoV-2 spike (S), two commercially available chemiluminescence assays Ortho VITROS Immunodiagnostic Products Anti-SARS-CoV-2 Total Reagent Pack and Abbott SARS-CoV-2 IgG assay and one commercially available Surrogate Virus Neutralization Test (sVNT), GenScript USA Inc., cPass SARS-CoV-2 Neutralization Antibody Detection Kit for the detection of SARS-CoV-2 specific antibodies. Using a panel of rRT-PCR confirmed COVID-19 patients' sera and a negative control group as a reference standard, all three immunoassays demonstrated high comparable positivity rates and low discordant rates. All three immunoassays were highly sensitive with estimated sensitivities ranging from 95.4-96.6 %. ROC curve analysis indicated that all three immunoassays had high diagnostic accuracies with area under the curve (AUC) values ranging from 0.9698 to 0.9807. High positive correlation was demonstrated among the conventional microneutralization test (MNT) titers and the sVNT inhibition percent values. Our study indicates that independent evaluations are necessary to optimize the overall utility and the interpretation of the results of serological tests. Overall, we demonstrate that all serological tests evaluated in this study are suitable for the detection of SARS-CoV-2 antibodies.

Keywords: COVID-19; SARS-CoV-2; antibodies; immunoassays; neutralization assay; serological tests.

Fig. 1.

Receiver Operating Characteristic (ROC) Curves for each Immunoassay. (a) ELISA Spike Ectodomain Total Ab, (b) Ortho VITROS Immunodiagnostic Products Anti-SARS-CoV-2 Total Reagent Pack Ab, (c) Abbott SARS-CoV-2 IgG Ab. Dashed lines represent assay performance at specific cut off values. An AUC of 0.9–1.0 is considered excellent, 0.8–0.9 very good, 0.7–0.8 good, 0.6–0.7 sufficient, <0.5 test not useful [24].

Fig. 2.

Correlational analysis of the numerical values obtained by each Immunoassay. (a) Abbott Index IgG values vs Ortho S/C Total Ab values, (b) ELISA Spike Ectodomain Total Ab S/T values vs Ortho S/C Total Ab values, (c) ELISA Spike Ectodomain Total Ab S/T values vs Abbott Index IgG values. Pearson correlation coefficient (r), and 95 % Confidence Interval (CI) are indicated for each immunoassay plotted against each other. Data are presented for 87 rRT-PCR confirmed SARS-CoV-2 specimens known as the positive reference standard and 117 negative specimens known as the negative reference standard. Signal to Calibrator, (S/C); Signal to Threshold (S/T).

Fig. 3.

Correlational analysis between microneutralization test (MNT) titers and Immunoassays numerical values. (a) Ortho S/C Total Ab values vs. MNT titer, (b) Abbott Index IgG values vs MNT titer, (c) ELISA Spike Ectodomain Total Ab S/T values vs MNT titer. Pearson correlation coefficient (r), and 95 % Confidence Interval (CI) are indicated for each immunoassay values plotted against the MNT titer. Data are presented for 87 rRT-PCR confirmed SARS-CoV-2 specimens known as the positive reference standard and 117 negative specimens known as the negative reference standard.

Fig. 4.

Surrogate Virus Neutralization Test (sVNT) performance analysis. (a) ROC curve for sVNT, (b) Correlational Analysis between sVNT percent inhibition and MNT titer. Pearson correlation coefficient (r), and 95 % Confidence Interval (CI) are indicated for each sVNT percent inhibition values plotted against the MNT titer. Data are presented for 87 rRT-PCR confirmed SARS-CoV-2 specimens known as the positive reference standard and 117 negative specimens known as the negative reference standard. Dashed lines represent assay performance at specific cut off values. An AUC of 0.9–1.0 is measured as being excellent, 0.8–0.9 very good, 0.7–0.8 good, 0.6–0.7 sufficient, <0.5 test not useful [24].