key: cord-0926069-l7kvv2xe authors: Findeisen, Peter; Stiegler, Hugo; Lopez-Calle, Eloisa; Schneider, Tanja; Urlaub, Eva; Hayer, Johannes; Zemmrich, Claudia title: Clinical Performance Evaluation of a SARS-CoV-2 Rapid Antibody Test for Determining Past Exposure to SARS-CoV-2 date: 2020-11-20 journal: Int J Infect Dis DOI: 10.1016/j.ijid.2020.11.164 sha: d1b77ce5c42cf3ee63a776131bef62355a85eea1 doc_id: 926069 cord_uid: l7kvv2xe OBJECTIVES: The true prevalence and seropositivity of SARS-CoV-2 infection remains unknown, due to the number of asymptomatic infections and limited access to high-performance antibody tests. To fill this gap, the clinical performance of a point-of-care SARS-CoV-2 Rapid Antibody Assay, a chromatographic immunoassay for detection of IgM/IgG antibodies, in near-patient settings was assessed. METHODS: 42 Anti-SARS-Cov-2 positive (CoV+) and 92 Anti-SARS-Covid-2 negative (CoV-) leftover samples from before December 2019 were assessed, using the Elecsys® Anti-SARS-CoV-2 as the reference assay. Analytical specificity was tested using leftover samples collected before December 2019 from patients with common cold symptoms. RESULTS: The SARS-CoV-2 Rapid Antibody Test was 100.0% (95% CI 91.59–100.00) sensitive and 96.74% (95% CI 90.77–99.32) specific, with 0.00% assay failure rate. No cross-reactivity was observed against the common cold panel. Method comparison was additionally conducted by two external laboratories, using 100 CoV+/275 CoV- samples, also comparing whole blood versus plasma matrix. The comparison demonstrated 96.00% positive/96.36% negative percent agreement for plasma with the Elecsys Anti-SARS-CoV-2 and 99.20% percent overall agreement between whole blood and EDTA plasma. CONCLUSION: The SARS-CoV-2 Rapid Antibody Test demonstrated similar performance to the manufacturer’s data and a centralized automated immunoassay, with no cross-reactivity with common cold panels. The global COVID-19 pandemic created an urgent unmet clinical need to investigate reliable diagnostic tools for patients, as well as understand the extent of exposure and spread of infection among wider populations (Centers for Disease Prevention and Control, 2020, European Centre for Disease Prevention and Control, 2020a, The World Health Organization, 2020) . Acute diagnosis of the COVID-19 infection is based on identification of viral RNA via PCR from swab samples, which is detectable from symptom onset for approximately four weeks . As is known from localized testing during outbreaks, many people who are infected with the virus do not present with any clinical symptomscurrent estimates suggest around 30% of seropositive individuals are asymptomatic (Mizumoto et al., 2020 , Pollan et al., 2020 , Sandri et al., 2020 . Those individuals carry the virus and potentially spread it to others, who may react with a severe COVID-19 disease . No region in the world can perform PCR testing of every patient with common cold symptoms or who has had contact with a suspected COVID-19 patient. In addition to clinical testing of individuals with suspected COVID-19 for direct virus detection, surveillance strategies need to combine several diagnostic techniques to monitor disease kinetics in wider populations (European Centre for Disease Prevention and Control, 2020a, World Health Organization, 2020) . To control the pandemic, it seems crucial to investigate who has already had an infection and has developed antibodies as an immune response, and vice versa, who is still vulnerable to an infection (Althoff et al., 2020 , Fiore et al., 2020 , MacIntyre, 2020 , Sen-Crowe et al., 2020 , Steinbrook, 2020 . Antibody tests are not intended to diagnose an acute COVID-19 infection, more specific diagnostic methods should be performed to obtain this (European Centre for Disease Prevention and Control, 2020a ). Ongoing research on the level and duration of immunity J o u r n a l P r e -p r o o f of seropositive persons will add further value to the clinical and epidemiological interpretation of positive antibody testing results. Preliminary data suggest that high affinity antibody tests show good correlation with neutralizing activity (Wu et al., 2020) . Based on current evidence, immunoglobulin M (IgM) antibodies are detectable within 5 days after symptom onset and immunoglobulin G (IgG) antibodies within 5-7 days (Guo et al., 2020 , Long et al., 2020 , Lou et al., 2020 , Okba et al., 2020 , Sethuraman et al., 2020 , Zhang et al., 2020 , Zhao et al., 2020 . Depending on the applied method, seroconversion is observed after a median of 10-13 days after symptom onset for IgM and 12-14 days for IgG, and maximum for both is reached after 2 weeks (Amanat et al., 2020 , Guo et al., 2020 , Long et al., 2020 , Lou et al., 2020 , Okba et al., 2020 , Sethuraman et al., 2020 , Xiang et al., 2020 , Zhang et al., 2020 , Zhao et al., 2020 . Individual levels and kinetics of both IgM and IgG are highly variable, which is why simultaneous detection of both is recommended. Currently available rapid antibody tests require improved accuracy before being recommended by competent authorities and used by healthcare professionals (HCPs) in the wider population (Centers for Disease Prevention and Control, 2020, European Centre for Disease Prevention and Control, 2020a). The US Food and Drug Administration (FDA) released technical requirements for antibody tests on April 4, 2020, that include a specificity of ≥ 95% and cross-reactivity testing for common cold and other coronaviruses (US, 2020). There are different high-throughput Anti-SARS-CoV-2 antibody tests available; the assay selected as the reference for our test (Elecsys Anti-SARS-CoV-2 Immunoassay) is based on electrochemiluminescence (ECLIA), using a double-antigen sandwich test principle and a recombinant protein representing the antigen for the determination of antibodies to SARS-CoV-2, namely the nucleocapsid protein (N) (Roche Diagnostics GmbH, 2020). It provides a qualitative result with a J o u r n a l P r e -p r o o f sensitivity of 100.0% (95% CI 88.10-100.0) at ≥ 14 days after PCR confirmation and a specificity of 99.81% (95% CI 99.65-99.91) . Rapid tests, also called point-of-care (PoC) tests, combine immunoassay and chromatography for a qualitative detection of antibodies. The selected test (Anti-SARS-CoV-2 Rapid Antibody Test [SD Biosensor, Chungcheongbuk-do, Republic of Korea] ) is a CE marked lateral flow assay displaying a visual 'yes/no' answer for the selective detection of specific IgG and/or IgM antibodies to SARS-CoV-2, with two separate colored bands for IgG and IgM (SD Biosensor, 2020) . The manufacturer states the specificity is 98.65% and sensitivity beyond 14 days after symptom onset of 99.03%, tested on 103 PCR-confirmed CoV+ and 222 CoV-samples (SD Biosensor, 2020) . The samples had also been tested for early sensitivity between 7 and 14 days after symptom onset with a result of 92.59%. SD Biosensor has performed several cross-reactivity studies involving numerous specimens, including influenza A and B. In this study series, we further validated and extended the manufacturers' clinical performance and cross-reactivity data, by performing a matrix and method comparison to expand the limited external data and gain additional data on the overall assay performance. The assay (Figure 1 ) needs 10 µl human serum or plasma, or 20 µl whole venous or capillary blood sample to be filled into the preformed well of the test device. Three pre-coated lines mark the "C" control line, and the "G" and "M" test lines for IgG and IgM. The control line is used as procedural control and should always appear if the test procedure is performed properly and the test reagents are working. According to the instructions for use the assay should be read between 10-15 minutes after addition of test materials. A performance analysis was conducted at Roche Diagnostics (Penzberg, Mannheim, Germany) using 42 Elecsys Anti-SARS-CoV-2 confirmed CoV+ and 92 leftover samples from healthy donors, collected before December 2019 and additionally confirmed by the Elecsys Anti-SARS-CoV-2 CoV-(56 lithium heparin plasma, 36 EDTA plasma). Crossreactivity testing was conducted with 18 samples from individuals expressing signs and symptoms of common cold (i.e. sore throat, cough, fever) collected before December 2019. Additional matrix equivalence and read-out time analysis captured 159 Elecsys The assay presented a qualitative visual test result without the need for a read-out instrument like other rapid antibody devices on the market. Some lines were quite faint, A total of 10 EDTA samples and 11 whole blood samples were detected antibody positive by the Anti-SARS-CoV-2 Rapid Antibody Assay but antibody negative by the Elecsys assay, see Table 4a for the respectively detected immunoglobulin classes and the respective signal intensity on the 11 rapid tests. 96 plasma and 94 whole blood samples out of 100 Elecsys-positive samples were detected positive by the rapid test, see Table 4b for the respective immunoglobulin classes and signal intensity of the six rapid test results. The matrix comparison for the Anti-SARS-CoV-2 Rapid Antibody Assay found of 106 plasma samples with an antibody positive test result, included two samples which had negative tests results with whole blood. One out of 269 negative test results on the rapid test with plasma displayed a positive result with whole blood. The COVID-19 pandemic has created an urgent need for antibody testing of large populations to determine seroprevalence and potential immunity, which will be of more importance if more conclusive scientific data on correlation between these factors become available (Centers for Disease Prevention and Control, 2020, European Centre for Disease Prevention and Control, 2020a , Ozcurumez et al., 2020 , Theel et al., 2020 , Zhang et al., 2020 (Biosensor, 2020) . A limitation of this study is that samples were not At the time of writing this manuscript, few studies exist demonstrating the performance of the rapid antibody tests external to the manufacturers (Batra et al., 2020 , Jaaskelainen et al., 2020 , Minteer et al., 2020 , Naranbhai et al., 2020 , Pallett et al., 2020 . The intention of the study was to add real-world clinical evidence for a rapid antibody test. For SARS- CoV-2 tests high specificity is a priority, particularly in low prevalence settings (30), as such it would be interesting to further evaluate the interpretation of the low positive samples at the rapid test, particularly for samples that were IgM positive only, to determine if these reflect non-specific binding, or true early detection. Further assessment with serial samples taken from COVID-19 patients from early infection phase onwards will help to better understand this. The investigated Anti-SARS-CoV-2 Rapid Antibody Test provided readily evaluable results, regardless of sample type (whole blood or EDTA plasma) and independent of any read-out time between 10 and 15 minutes, as stated in the instructions for use. Those positive practical aspects could enable potential use outside medical environments. The assay is currently intended for professional use in laboratory and PoC environments as an aid in identifying individuals with an adaptive immune response to SARS-CoV-2, indicating prior infection. In these studies, the SARS-CoV-2 Rapid Antibody Test demonstrates excellent clinical performance without cross-reactivity to common cold samples and results comparable to data of an automated high-performance immunoassay (Elecsys). Our data confirm and extend the manufacturers' performance data and add further details on matrix and method comparisons. Whilst further assessments in the future will be valuable, this study supports the use of the SARS-CoV-2 Rapid Antibody Test as a reliable diagnostic instrument for SARS-CoV-2 IgM and IgG antibody detection in nearpatient settings with potential extended usability outside medical environments. acquisition in the laboratory and preliminary data analysis. 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