Table 5.
Titer comparison of the WHO international reference panel for anti-SARS-CoV-2 immunoglobulins.
| Antibody Titer (NIBSC Code) |
NIBSC BAU/mL (Anti-S1 IgG) |
COVID-19 SIA MFI a (Anti-S1 IgG) |
Plot b BAU/mL |
COVID-19 SIA c BAU/mL |
|---|---|---|---|---|
| Low (20/149) | 46 | 468 | 0.39 | 39 |
| Low S, High N (20/144) | 50 | 618 | 0.59 | 59 |
| Mid (20/148) | 246 | 2352 | 2.8 | 280 |
| High (20/150) | 766 | 4052 | 6.14 | 614 |
| Negative (20/142) | ND | 9 d | ND | ND |
a Dilution: 1:100; b Estimated from Figure 3; c Estimated concentration in original sample; d Cut-off for seropositivity = 300 MFI; COVID-19, Coronavirus disease 2019; SIA, suspension immunoassay; S1, spike subunit 1; RBD, receptor binding domain; BAU, binding antibody unit, ND, not determined.