Chemiluminescent microparticle assay for anti-SARS-CoV-2 RBD IgG and anti-NP of ancestral strain
Plasma samples were isolated using sodium citrate and stored at -80°C. A chemiluminescent microparticle assay (CMIA) was used to determine anti-RBD and anti-NP through SARS-CoV-2 IgG II Quant (Abbott Laboratory System, Illinois, US) on the ARCHITECT i System. Antibody levels were linearly measured between 21.0-40,000.0 arbitrary units per mL (AU/mL), and subsequently converted to binding antibody units per mL (BAU/mL) per WHO’s International Standards and an equation provided by the manufacturer (BAU/mL = 0.142 × AU/mL). Seropositivity was defined by cutoff values ≥ 50 AU/mL (7.1 BAU/mL). Antibody response against SARS-CoV-2 NP protein was determined using baseline plasma samples through CMIA SARS-CoV-2 IgG (Abbott, List No. 06R86) on the ARCHITECT i System.