Table 2. Performance of ELISA tests as estimated by ROC analysis.

Performance measures	ELISA assay
	RBD(1)-IgG	RBD-IgM	Spike(2)-IgG	Spike-IgM
AUC(3) (95% CI)	0.995 (0.99–1)	0.987 (0.969–1)	0.98 (0.95–1)	0.986 (0.972–1)
AUC standard error	0.002	0.009	0.015	0.007
Optimal cut-off(4)	0.483	0.933	0.646	0.847
Sensitivity (95% CI)	0.990 (0.946–0.999)	0.970 (0.917–0.992)	0.941 (0.858–0.976)	0.929 (0.845–0.969)
Specificity (95% CI)	0.933 (0.821–0.977)	0.977 (0.884–0.998)	0.977 (0.884–0.998)	0.955 (0.851–0.992)
PPV(5) (95% CI)	0.971 (0.918–0.992)	0.990 (0.945–0.999)	0.984 (0.917–0.999)	0.970 (0.899–0.994)
NPV(6) (95% CI)	0.976 (0.879–0.998)	0.936 (0.828–0.978)	0.916 (0.804–0.967)	0.895 (0.778–0.954)
Kappa (7) (95% CI)	0.935 (0.873–0.998)	0.937 (0.876–0.998)	0.909 (0.831–0.987)	0.874 (0.784–0.964)
Kappa SE	0.032	0.031	0.040	0.046

(¹) RBD, recombinant SARS-CoV-2 Receptor Binding Domain.

(²) Spike, recombinant SARS-CoV-2 Spike protein.

(³) AUC, area under the ROC curve.

(⁴) Calculated by Youden method.

(⁵) Positive Predictive Value.

(⁶) Negative Predictive Value.

(⁷) Agreement with RT-PCR assay.