TABLE 1.
Thresholds, clinical specificity, and clinical sensitivity of FMIA measuring SARS-CoV-2 antibodies from convalescent-phase seraa
| Antibody | FMIA threshold (U/mL) | WHO standard adjusted threshold (BAU/mL) | DPO of optimal sensitivity | Specificity (%) (95% CIb) (nc) | Sensitivity (%) (95% CIb) (nd) |
|---|---|---|---|---|---|
| IgG | SFL ≥ 0.388 and RBD ≥ 0.712 | SFL ≥ 0.089 and RBD ≥ 0.13 | 13–150 | 100 (99.1–100) (402) | 100 (97.3–100) (140) |
| IgA | SFL ≥ 3.88 and RBD ≥ 11.4 | 13–36 | 100 (99.1–100) (402) | 100 (94.7–100) (69) | |
| IgM | SFL ≥ 17.5 | 13–28 | 100 (99.1–100) (402) | 100 (91.0–100) (39) |
a
RBD, receptor binding domain of SARS-CoV-2 (Wuhan-Hu-1) spike glycoprotein; SFL, full-length spike glycoprotein of SARS-CoV-2 (Wuhan-Hu-1); DPO, days post-onset of symptoms.
b
Wilson confidence interval.
c
Number of negative samples used for calculations.
d
Number of positive samples used for calculations, which includes only part of the positive serum panel and differs between antibody classes due to exclusion of samples that did not meet DPO of optimal sensitivity criteria.