Table 3.

Conversion factors calibrating the multiplex SARS‐CoV‐2 ECL serology assay arbitrary units (AU mL⁻¹) to the WHO International Reference Standard units (BAU mL⁻¹)

SARS‐CoV‐2 antigen	WHO International Standard
	Conversion factor (AU mL−1 to BAU mL−1)	95% CI
S	0.00645	0.00594–0.00701
RBD	0.00798	0.00735–0.00866
N	0.00324	0.00295–0.00356

AU, arbitrary units; BAU, binding arbitrary units; CI, confidence interval; ECL, electrochemiluminescence; N, nucleocapsid protein; RBD, receptor‐binding domain; S, spike protein; SARS‐CoV‐2, severe acute respiratory syndrome coronavirus 2; WHO, World Health Organization.