Liaison sars cov 2 trimerics igg chemiluminescent immuno assay

Quantitative evaluation of SARS-CoV-2 IgG anti-spike (S) glycoprotein antibodies was performed by the Liaison^® SARS-CoV-2 TrimericS IgG chemiluminescent immuno-assay (CLIA) on the Liaison XL (Diasorin^® S.P.A., Saluggia, Italy), according to the manufacturer’s instructions. The cut-off for positivity was 33.8 binding activity units (BAU)/mL. This assay showed an optimal correlation with the micro-neutralization test (negative and positive agreement of 100% and 96.9%, respectively) and was standardized against the WHO internal standard [42 (link)]. Regarding analytical performance, high sensitivity (98.7%) together with high specificity (99.5%) ensure accurate results. Samples containing levels of IgG anti-S antibodies above the measurement range (>2080 BAU/mL) were further diluted 1:10 using LIAISON^® TrimericS IgG Diluent. In order to exclude previous SARS-CoV-2 asymptomatic infection during the overall period considered, the anti-N response was determined using the Roche Elecsys^® Anti-SARS-CoV-2 electro-chemiluminescence immuno-assay (ECLIA) on the Cobas e 601 module (Roche^®, Mannheim, Germany).

Humoral immune response was evaluated at each time point using the Liaison^® SARS-CoV-2 TrimericS IgG chemiluminescent immunoassay (CLIA) on the Liaison XL (Diasorin S.P.A., Saluggia, Italy) according to the manufacturer’s instructions and using the manufacturer’s cut-off for positivity of 33.8 binding activity units (BAU)/mL. This assay quantitatively determines antibodies against the TrimericS complex, which includes the Receptor Binding Domain (RBD) and N-terminal domain (NTD) sites including S1 and S2. Samples above the measuring range of 2000 BAU/mL for anti-S were further diluted 1:10 using the Diasorin assay manual diluent to achieve exact analytical measurement. The assay is correlated with the micro-neutralization and standardized against the WHO internal standard (NIBSC 20-136) (24 (link)).
The quantitative detection of serum IgG antibodies to the nucleocapsid (N) protein of SARS-CoV-2 was performed on all subjects positive for IgG anti-S1 at T0, using a chemiluminescent micro-particle immunoassay (CMIA) on the Abbott Architect i2000SR analyser using the manufacturer’s cut-off for positivity of 1.4 S/CO (SARS-CoV-2 IgG Quant assay, Abbott, Lake Forest Illinois, USA).