key: cord-0760399-wcqdksfg authors: Favresse, Julien; Eucher, Christine; Elsen, Marc; Marie, Tré-Hardy; Dogné, Jean-Michel; Douxfils, Jonathan title: Clinical performance of the Elecsys electrochemiluminescent immunoassay for the detection of SARS-CoV-2 total antibodies date: 2020-06-02 journal: Clin Chem DOI: 10.1093/clinchem/hvaa131 sha: 0cc9e0b19ec46440f0a90209d66a0e75659326cc doc_id: 760399 cord_uid: wcqdksfg nan In the context of COVID-19, a wide range of serology immunoassays with different SARS-CoV-2 antigen recognition and antibody specificity have been developed to complement RT-PCR assays [1] . Serological testing is useful for diagnosis and characterization of the course of the disease, identification of convalescent plasma donors, for epidemiology studies, lockdown exit programs and COVID-19 vaccine development [2, 3] . Due to the widespread dissemination of these new methods and the limited experience with these assays, it is crucial for laboratories to rigorously validate these methods before broad introduction into routine clinical practice. Independent validations are also needed to assure the assays are in line with expected analytical and clinical performance specifications [1] [2] [3] [4] . This study is the first to report the external validation of a new electrochemiluminescent immunoassay (ECLIA) test, the Elecsys anti-SARS-CoV-2 from Roche Diagnostics ® . This test allows the detection of total antibodies (including IgG) specifically directed against SARS-CoV-2 nucleocapsid and is performed on the cobas ® e801 module. The test result is given as a cut-off index (COI). According to the manufacturer, a result <1.0 is considered negative while a result ≥1.0 is considered positive [5] . The within-run and between-run imprecision (CV) on 5 patient pools (COI means of 0.081, 1.0, 8.7, 24, and 54) varied from 0.8% to 3.3%, and from 1.2% to 3.6%, respectively. Sample storage complied with the conditions listed in the package insert. This retrospective study was conducted from May 6 to 12, 2020 at the clinical biology Analyses of serum samples obtained 28 days or more after symptom onset provided a sensitivity of 96.7% (95%CI: 82.8-99.9%) and 100% (95%CI: 88.9-100%) with the manufacturer and the optimized cut-off, respectively (Figure 1) . Considering samples obtained before 14 days (from RT-PCR + or symptoms onset), sensitivities were not sufficient to be reliable in clinical practice (Figure 1) . (i.e.>0.165) had no effect on the measured diagnostic specificity (Figure 1) . The optimal ROC cut-off showed excellent clinical performance 14 days or more following RT-PCR positivity or following the onset of COVID-19 symptoms. Additional studies are needed to further confirm the best cut-off. Expert societies are also urged to provide guidance on the best time after RT-PCR positivity or symptom onset to perform serological investigations, since this is an important determinant of the true positivity rate. We wish to thank the personnel of the Saint-Luc Bouge laboratory for its technical assistance. The dotted lines indicate the manufacturer's cut-off (in black) and the optimized cut-off (in grey). Vitro Diagnostic Assays for COVID-19: Recent Advances and Emerging Trends The important role of serology for COVID-19 control SARS-CoV-2 Serology: Much Hype, Little Data. Clin [epub ahead of print COVID-19 and Postinfection Immunity: Limited Evidence, Many Remaining Questions Elecsys Anti-SARS-CoV-2, insert sheet REF 09203079190 Author Contributions: All authors confirmed they have contributed to the intellectual content of this paper and have met the following 4 requirements: (a) significant contributions to the conception and design, acquisition of data, or analysis and interpretation of data; (b) drafting or revising the article for intellectual content; (c) final approval of the published article; and (d) agreement to be accountable for all aspects of the article thus ensuring that questions related to the accuracy or integrity of any part of the article are appropriately investigated and resolved.J. Favresse, statistical analysis, administrative support, provision of study material or patients; C. Eucher, administrative support, provision of study material or patients; M. Elsen, administrative support, provision of study material or patients; J. Douxfils, statistical analysis.