Abstract and Introduction
Objectives: Serologic testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has experienced a changing landscape of available assays coupled with uncertainty surrounding performance characteristics. Studies are needed to directly compare multiple commercially available assays.
Methods: Residual serum samples were identified based on SARS-CoV-2 reverse transcription polymerase chain reaction (RT-PCR) testing, clinical test results, and collection dates. Serum samples were analyzed using assays from four different manufacturers: DiaSorin anti–SARS-CoV-2 S1/S2 IgG, EUROIMMUN anti–SARS-CoV-2 IgG ELISA, Roche Elecsys anti–SARS-CoV-2, and Siemens SARS-CoV-2 Total antibody assays.
Results: Samples from SARS-CoV-2 RT-PCR–positive patients became increasingly positive as time from symptom onset increased. For patients with latest sample 14 or more days after symptom onset, sensitivities reached 93.1% to 96.6%, 98.3%, and 96.6% for EUROIMMUN, Roche, and Siemens assays, respectively, which were superior to the DiaSorin assay at 87.7%. The specificity of Roche and Siemens assays was 100% and superior to DiaSorin and EUROIMMUN assays, which ranged from 96.1% to 97.0% and 86.3% to 96.4%, respectively.
Conclusions: Laboratories should be aware of the advantages and limitations of serology testing options for SARS-CoV-2. The specificity and sensitivity achieved by the Roche and Siemens assays would be acceptable for testing in lower-prevalence regions and have the potential of orthogonal testing advantages if used in combination.
Clinical laboratory serologic testing for antibodies directed against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19), has been beset by a series of problems. Serologic tests were initially allowed to be distributed by any manufacturer, although some claims were lacking in quality, leading to removal from the US Food and Drug Administration (FDA) "notification list" of assays with pending or approved emergency use authorization. As more manufacturers with established in vitro diagnostics history have released serology assays with larger premarket studies, the presumption is that more consistent and high-quality assays are available. Many SARS-CoV-2 serology assay manufacturers report impressive performance results, which are summarized by the FDA based on review of submitted data. However, given a paucity of real-world and consistent evaluations of these assays, the FDA has partnered with the National Institutes of Health and Centers for Disease Control and Prevention (CDC) to perform limited independent evaluations of some assays. Although there are multiple evaluations of SARS-CoV-2 serology assays,[4–22] there is a relative paucity of robust evaluations of more recently released tests. As such, there is need for greater direct comparisons across multiple, different platforms. Many laboratories have little real-word information about performance limitations when choosing among assays.
The best use of SARS-CoV-2 serologic testing remains an open question. Regardless of whether clinical or epidemiologic use is planned, the predictive values are important to consider, particularly in areas with low pretest probability (eg, mass screening). Both the throughput of an assay and in particular its specificity are crucial parameters for clinical laboratory implementation if large-scale serology testing is desirable in a low-prevalence environment.
Approaches for anti–SARS-CoV-2 immunoassays involve differing antigens (eg, nucleocapsid vs spike protein and full-length vs subdomains) and/or immunoglobulin isotypes (eg, immunoglobulin G [IgG], immunoglobulin M [IgM], total). A preferred combination may evolve depending on the desired purpose of testing as our understanding of COVID-19 matures, including breadth and duration of antibody responses, neutralizing effects of antibodies, and antigen choices for vaccines. It is possible that appropriate assays for detection of prior viral infection may be different from those to confirm a vaccine response.
Given the uncertain and shifting landscape for clinical laboratories, we sought to compare a common set of serum samples across four commercial assays as part of our evaluation for potential implementation of high-throughput testing. These findings will help inform the strengths and limitations of each assay in a directly comparable manner.
Am J Clin Pathol. 2021;155(2):267-279. © 2021 American Society for Clinical Pathology