Spike vs nucleocapsid SARS-CoV-2 antigen detection: application in nasopharyngeal swab specimens

• DOI: 10.1007/s00216-021-03298-4
• Publication Date: 2021-03-25T22:57:59Z
• Authors: Moria Barlev-Gross; Shay Weiss; Amir Ben-Shmuel; Assa Sittner; Keren Eden; Noam Mazuz; Itai Glinert; Elad Bar-David; Reut Puni; Sharon Amit; Or Kriger; Ofir Schuster; Ron Alcalay; Efi Makdasi; Eyal Epstein; Tal Noy-Porat; Ronit Rosenfeld; Hagit Achdout; Ohad Mazor; Tomer Israely; Haim Levy; Adva Mechaly
• Keywords: 0301 basic medicine; SARS-CoV-2; COVID-19; Enzyme-Linked Immunosorbent Assay; Phosphoproteins; Sensitivity and Specificity; COVID-19 Serological Testing; Specimen Handling; 3. Good health; 03 medical and health sciences; Spike Glycoprotein, Coronavirus; Coronavirus Nucleocapsid Proteins; Humans; Research Paper

AbstractPublic health experts emphasize the need for quick, point-of-care SARS-CoV-2 detection as an effective strategy for controlling virus spread. To this end, many “antigen” detection devices were developed and commercialized. These devices are mostly based on detecting SARS-CoV-2’s nucleocapsid protein. Recently, alerts issued by both the FDA and the CDC raised concerns regarding the devices’ tendency to exhibit false positive results. In this work we developed a novel alternative spike-based antigen assay, comprised of four high-affinity, specific monoclonal antibodies, directed against different epitopes on the spike’s S1 subunit. The assay’s performance was evaluated for COVID-19 detection from nasopharyngeal swabs, compared to an in-house nucleocapsid-based assay, composed of antibodies directed against the nucleocapsid. Detection of COVID-19 was carried out in a cohort of 284 qRT-PCR positive and negative nasopharyngeal swab samples. The time resolved fluorescence (TRF) ELISA spike-assay displayed very high specificity (99%) accompanied with a somewhat lower sensitivity (66% for Ct<25), compared to the nucleocapsid ELISA assay which was more sensitive (85% for Ct<25) while less specific (87% specificity). Despite being out-performed by qRT-PCR, we suggest that there is room for such tests in the clinical setting, as cheap and rapid pre-screening tools. Our results further suggest that when applying antigen detection, one must consider its intended application (sensitivity vs specificity), taking into consideration that the nucleocapsid might not be the optimal target. In this regard, we propose that a combination of both antigens might contribute to the validity of the results.Abstract FigureGraphic abstractSchematic representation of sample collection and analysis. The figure was created using BioRender.com