Abstract
While lateral flow test formats can be utilized with whole blood and low sample volumes, their diagnostic characteristics are inferior to immunoassays based on chemiluminescence immunoassay (CLIA) or enzyme-linked immunosorbent assay (ELISA) technology. CLIAs and ELISAs can be automated to a high degree but commonly require larger serum or plasma volumes for sample processing. We addressed the suitability of EDTA-anticoagulated whole blood as an alternative sample material for antibody testing against SARS-CoV-2 by electro-CLIA (ECLIA; Roche, Rotkreuz, Switzerland) and ELISA (IgG and IgA; Euroimmun, Germany). Simultaneously drawn venous serum and EDTA-anticoagulated whole blood samples from 223 individuals were included. Correction of the whole blood results for hematocrit led to a good agreement with the serum results for weakly to moderately positive antibody signals. In receiver-operating characteristic curve analysis, all three assays displayed comparable diagnostic accuracy (area under the curve (AUC)) using corrected whole blood and serum (AUCs: 0.97 for ECLIA and IgG ELISA; 0.84 for IgA ELISA). In conclusion, our results suggest that the investigated assays can reliably detect antibodies against SARS-CoV-2 in hemolyzed whole blood anticoagulated with EDTA. Correction of these results for hematocrit is suggested. This study demonstrates that the automated processing of whole blood for identification of SARS-CoV-2 antibodies with common ECLIA and ELISA methods is accurate and feasible.
Highlights
The coronavirus disease 2019 (COVID-19) constitutes a recent global pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus
Paired serum and EDTA-whole blood samples were available from 223 patients (112 females, 50%; 95% confidence intervals (CIs): 44, 57)
COVID-19 was diagnosed in 110 patients (49%; 95% CI: 43, 56) with either reverse transcriptase polymerase chain reaction (RT-PCR) (n = 72) or two positive antibody results in one assay against the N-antigen and one assay against the S-antigen (IgG or IgA; n = 38)
Summary
The coronavirus disease 2019 (COVID-19) constitutes a recent global pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. Whereas acute disease diagnosis by laboratory methods predominantly utilizes demonstration of virus replication by real-time reverse transcriptase polymerase chain reaction (RT-PCR), serologic tests are mainly employed for diagnosis of past COVID-19 infection [1,2,3,4,5,6,7,8,9]. Demonstration of specific antibodies against the SARS-CoV-2 allows for confirmation of clinically suspected COVID-19 cases for which RT-PCR testing has been negative [1,10]. The specificity of antibodies against the SARS-CoV-2 is directed against several virus-specific proteins, such as the nucleocapsid (N) or spike (S) proteins [12,13]. RBD-binding enables the SARS-CoV-2 to infect the target cell via the angiotensin-converting enzyme 2 (ACE2) receptor [17]
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