Longitudinal Assessment of SARS-CoV-2 Antinucleocapsid and Antispike-1-RBD Antibody Testing Following PCR-Detected SARS-CoV-2 Infection

• Published in: The journal of applied laboratory medicine 2021-07, Vol.6 (4), p.1005-1011
• Main Authors: El-Khoury, Joe M, Schulz, Wade L, Durant, Thomas J S
• Format: Article
• Language: English
• Subjects: Antibodies, Viral - blood; Antibodies, Viral - immunology; COVID-19 - blood; COVID-19 - diagnosis; COVID-19 - genetics; COVID-19 - virology; COVID-19 Testing - methods; Europe; Humans; Longitudinal Studies; Nucleocapsid - immunology; Polymerase Chain Reaction - methods; Predictive Value of Tests; Reagent Kits, Diagnostic; SARS-CoV-2 - genetics; SARS-CoV-2 - immunology; SARS-CoV-2 - isolation & purification; Spike Glycoprotein, Coronavirus - immunology; United States
• ISSN: 2576-9456; 2475-7241
• DOI: 10.1093/jalm/jfab030

SARS-CoV-2 serologic assays are becoming increasingly available and may serve as a diagnostic aid in a multitude of settings relating to past infection status. However, there is limited literature detailing the longitudinal performance of EUA-cleared serologic assays in US populations, particularly in cohorts with a remote history of PCR-confirmed SARS-CoV-2 infection (e.g., >2 months). We evaluated the diagnostic sensitivities and specificities of the Elecsys® Anti-SARS-CoV-2 (anti-N) and Elecsys Anti-SARS-CoV-2 S (anti-S1-RBD) assays, using 174 residual clinical samples up to 267 days post-PCR diagnosis of SARS-CoV-2 infection (n = 154) and a subset of samples obtained prior to the COVID-19 pandemic as negative controls (n = 20). The calculated diagnostic sensitivities for the anti-N and anti-S1-RBD assays were 89% and 93%, respectively. Of the 154 samples in the SARS-CoV-2-positive cohort, there were 6 discrepant results between the anti-N and anti-S1-RBD assays, 5 of which were specimens collected ≥200 days post-PCR positivity and only had detectable levels of anti-S1-RBD antibodies. When only considering specimens collected ≥100 days post-PCR positivity (n = 41), the sensitivities for the anti-N and anti-S1-RBD assays were 85% and 98%, respectively. The anti-S1-RBD assay demonstrated superior sensitivity at time points more remote to the PCR detection date, with 6 more specimens from the SARS-CoV-2-positive cohort detected, 5 of which were collected more than 200 days post-PCR positivity. While analytical differences and reagent lot-to-lot variability are possible, this may indicate that, in some instances, anti-S1-RBD antibodies may persist longer in vivo and may be a better target for detecting remote SARS-CoV-2 infection.