Clinical evaluation of five different automated SARS-CoV-2 serology assays in a cohort of hospitalized COVID-19 patients

Abstract

Background: The global market for SARS-CoV-2-immunoassays is becoming ever more crowded with antibody-tests of various formats, targets and technologies, careful evaluation is crucial for understanding the implications of individual test results. Here, we evaluate the clinical performance of five automated immunoassays on a set of clinical samples.

Methods: Serum/plasma samples of 75 confirmed COVID-19 patients and 320 pre-pandemic serum samples of healthy blood donors were subjected to two IgG and three total antibody SARS-CoV-2-immunoassays. All test setups were automated workflows.

Results: Positivity of assays (onset of symptoms > 10 days) ranged between 68.4 % and 81.6 % (Diasorin 68.4 %, Euroimmun 70.3 %, Siemens 73.7 %, Roche 79.0 % and Wantai 81.6 %). All examined assays demonstrated high specificity of >99 % (Euroimmun, Diasorin: 99.1 %, Wantai: 99.4 %) but only two reached levels above 99.5 % (Roche: 99.7 %, Siemens 100 %). Interestingly, there was no overlap in false positive results between the assays. The strongest correlation of quantitative results was observed between the Diasorin and Euroimmun IgG tests (r² = 0.76). Overall, we observed no difference in the distribution of test results between female and male patients (p-values: 0.18-0.87). A significant difference between severely versus critically ill patients was demonstrated for the Euroimmun, Diasorin, Wantai and Siemens assays (p-values:0.041).

Conclusion: All assays showed good clinical performance. Our data confirm that orthogonal test strategies as recommended by the CDC can enhance clinical specificity. However, the suboptimal rates of test positivity found at time of hospitalization in this cohort underline the importance of molecular diagnostics to rule out/confirm active infection with SARS-CoV-2.

Keywords: COVID-19; SARS-CoV-2; Serology.

Fig. 1

Test results of examined SARS-CoV-2 serology assays. A-E The scatter plots with logarithmic scales display test results of SARS-CoV-2 PCR positive patients (blue dots, n = 75) and pre-pandemic blood donors (green dots, n = 320). Each dot represents one sample. Cut-off values for positivity are 1.1 for Euroimmun, 15 for Diasorin and 1 for Roche, Wantai and Siemens (upper dotted line). Cut-off values for borderline test results are 0.8 for Euroimmun and 12 for Diasorin (lower dotted line). F Test results of SARS-CoV-2 PCR positive patients (n = 75). Each column represents one patient. Samples are sorted by time since onset of symptoms in days. Negative test results are displayed in grey, positive test results in blue and borderline test results in light blue. Immunosuppressed patients are marked by a * in the bottom row and a ↑ in the bottom row indicates that RT-PCR was performed by an external certified lab. Abbreviations: A/C.O., absorbance/cut-off value; AU/mL, arbitrary units/mL; COI, cut-off index (signal sample/cut-off); d, days; Dia, Diasorin; Eur, Euroimmun; Roc, Roche; Ratio, ratio (extinction sample/extinction calibrator); Sie, Siemens; Wan, Wantai.

Fig. 2

Correlation between SARS-CoV-2 serology assays. A Scatter plots with logarithmic scales, each displaying the correlation between two tests. Test results of SARS-CoV-2 PCR positive patients (n = 75) are plotted. Each dot represents one sample. Dotted lines indicate assay cut-offs for positivity (upper line) and borderline test results (lower line). Values in dark blue areas tested positive in both assays and values in light blue areas in one assay. B Person correlation coefficients (r²) arranged in the same format as in A. Values are color-coded, with values close to 1 displayed in a dark blue and values close to 0 in a light blue. All correlations are significant (p-value: ≤0.0003). Abbreviations: A/C.O., absorbance/cut-off value; AU/ml, arbitrary units/mL; COI, cut-off index (signal sample/cut-off); D, Diasorin; E, Euroimmun; R, Roche; Ratio, ratio (extinction sample/extinction calibrator); S, Siemens; W, Wantai.