Sensitivity and performance of three novel quantitative assays of SARS-CoV-2 nucleoprotein in blood

Abstract

To assess if SARS-CoV-2 (COVID-19) systemic disease can be determined by available nucleoprotein assays, we compared the performance of three commercial SARS-CoV-2 nucleoprotein (N) assays in plasma. A total of 272 plasma samples collected in the period November–December 2021 were analyzed by the methods Simoa SARS CoV‐2 N Protein Advantage Kit [Quanterix Simoa], Solsten SARS-CoV-2 Antigen enzyme immunosorbent assay (ELISA) [Solsten ELISA], and Elecsys SARS‐CoV‐2 Antigen electrochemiluminescence immunoassay [Elecsys ECLIA]. Additionally, a dilution series of inactivated virus culture was analyzed by the three assays. The SARS CoV-2 PCR-status was not known for the patients. Linear correlation in the pairwise correlation between assays as well as linearity of dilution series of inactivated virus culture was estimated by Spearman score. Sensitivity and specificity were estimated by pairwise comparison. The three assays showed poor agreement on patient samples with regards to concentration. Performance on virus culture was excellent but with different level of detection (LOD). Positive vs negative results show comparable sensitivity and specificity of Quanterix Simoa and Solsten ELISA, with a higher LOD in Elecsys ECLIA and thus lower sensitivity and high specificity. N by all tested assays can be used as a marker for systemic COVID-19 disease.

Heterotypic responses against nsp12/nsp13 from prior SARS-CoV-2 infection associates with lower subsequent endemic coronavirus incidence

“…Nucleocapsid IgG reactivity was used to further classify some COVID-19 vaccine recipients that may have had prior SARS-CoV-2 infection. 32,33 Again as expected, nucleocapsid IgG levels were significantly higher in individuals with documented SARS-CoV-2 infection as compared to the two other groups (Figure 3B). We also examined the number of activated T cells (both CD4 + and CD8 + ) after exposure to various SARS-CoV-2 peptide pools using the activation induced marker (AIM) assay (Supplementary Figure 1).…”

Performance of Blood-Based Nucleocapsid Antigen Tests for Diagnosis of Severe Acute Respiratory Syndrome Coronavirus 2 Infection and Infectious Viral Shedding: A Systematic Review

“…The reasons for exclusion were as follows: the use of nasopharyngeal samples for N-antigen testing (n = 4), missing test performance characteristics (n = 3), or selection of the wrong population (n = 2; SARS-CoV-1). Ultimately, a total of 16 studies met our inclusion criteria [ 15–30 ]. A flow diagram describing the process is shown in Figure 1 .…”

Determining half-life of SARS-CoV-2 antigen in respiratory secretion

“…The antigen-based half-life assay is a test based on the destruction of the viral surface, which is different from cell culture and viral nucleic acid assays; therefore, direct detection of SARS-CoV-2 antigen may more appropriately reflect infectivity compared to RNA detection (Wang et al 2003a ; Peck Palmer et al 2023 ; Hillig et al 2023 ; Wang et al 2023b ); our results could be more reliable. Moreover, the half-life of the RNA determined by PCR could be more than the actual duration of infectivity.…”