Plasma specimens from coronavirus disease 2019 patients were double-tested for anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies by two different batches of MAGLUMI 2019-nCov immunoglobulin M/immunoglobulin G (IgM/IgG) assays to evaluate IgM/IgG levels, qualitative interpretation, antibody kinetics, and linearity of diluted specimen. Here we show that (i) high-level IgM specimens need to be diluted with negative human plasma but not kit diluents and (ii) measured anti-SARS-CoV-2 IgM/IgG concentrations are substantially higher with later marketed immunoassay batch leading to (iii) the change of qualitative interpretation (positive vs. negative) in 12.3% of specimens measured for IgM, (iv) the informative time-course pattern of antibody production only when data from different immunoassay batches are not combined.

Department of Anaesthesiology St Anne's University Hospital Brno Czech Republic

Department of Clinical Biochemistry University Hospital Brno Brno Czech Republic

Department of Clinical Microbiology and Immunology University Hospital Brno Brno Czech Republic

Department of Laboratory Medicine Masaryk Memorial Cancer Institute Brno Czech Republic

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