2.3. Antibody Titer Determination

Antibodies were determined by LIAISON^® SARS-CoV-2 S1/S2 IgG (DiaSorin- Italy), which uses chemiluminescence immunoassay (CLIA) technology for the quantitative determination of anti-S1 and anti-S2 specific IgG antibodies to SARS-CoV-2 in human serum or plasma samples. A cut-off of >15 AU/mL is resulted as positive, whereas <12 AU/mL is considered negative. Values between 12–15 AU/mL are considered equivocal or in the seroconversion phase. The assay is intended to support the study of the infected patient’s immune status by indicating the presence of neutralizing IgG antibodies against SARS-CoV-2. Positive results have a concordance of 94.4% with neutralizing antibodies. A cut-off value > 80 AU/mL on this assay correlate with neutralizing antibody titer levels of 1:160 on the neutralization test assay [18].

Antibody titer against SARS-CoV-2 assessment in the CP was done after CP was administered to the patients. Seven donors were found to have CP with negative antibody titers, and the patients who received those products were excluded from the analysis. In the rest (29 donors), IgG antibodies against SARS-CoV-2 were positive (>15 AU/mL). In 62.5% of the cases, the titer was >80 AU/mL, corresponding with neutralizing antibody titer levels of ≥1:160.