Comparison of two automated immunoassays for the detection of SARS-CoV-2 nucleocapsid antibodies

Abstract

Background

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel member of the coronavirus family that caused the global coronavirus 2019 (COVID-19) pandemic. The prevalence remains largely unknown because of early testing supply shortages. Although it cannot currently be used to determine level of immunity, antibody testing can contribute to epidemiological studies, identify convalescent plasma donors, or satisfy curiosity about previous exposure to the virus.

Methods

407 samples collected from hospitalized inpatients with and without a confirmed SARS-CoV-2 infection, 170 remnant clinical specimens collected and frozen prior to the COVID-19 outbreak, and paired serum and plasma samples from 23 convalescent plasma donors were used to determine performance characteristics of the Abbott SARS-CoV-2 IgG and Roche Elecsys Anti-SARS-CoV-2 assays. The sensitivity, specificity, imprecision, interferences, and sample stability were determined. These assays were then used to characterize the antibody response in serial samples from 20 SARS-CoV-2 positive inpatients.

Results

Both assays exhibited 100% specificity (95% CI; 99.05 – 100.00), giving no positive results in 170 specimens collected before July 2019 and 215 specimens from patients without a confirmed SARS-CoV-2 infection. Differences between platforms were most notable in SARS-CoV-2 positive samples. Roche offered higher sensitivity in convalescent plasma donors at 95.7% (95% CI; 78.1 – 99.9) versus 91.3% (95% CI; 72.0 – 98.9) but Abbott detected antibodies in two immunocompromised patients whereas Roche did not. The Roche and Abbott platforms also exhibited different trends in antibody signal for a subset of patients.

Conclusions

Both the Abbott and Roche platforms offer excellent specificity but different trends in antibody signal may reflect qualitative differences in the types of antibodies recognized by the two assays. Negative serologic results do not exclude previous SARS-CoV-2 infection.