Table 2.
Sensitivity and Specificity for Each Threshold Method and Isotype-Antigen Combination based on PCR-confirmed Hospitalized Coronavirus Disease 2019 Patients (n = 86) and Negative Samples (n = 96)
| Threshold Methoda | Antigen | IgA | IgG | IgM | |||
|---|---|---|---|---|---|---|---|
| Sensitivity, % | Specificity, % | Sensitivity, % | Specificity, % | Sensitivity, % | Specificity, % | ||
| 3 SD | RBD | 25.6 | 100.0 | 55.8 | 100.0 | 67.4 | 98.4 |
| S trimer | 75.6 | 100.0 | 76.7 | 100.0 | NA | NA | |
| N | 74.4 | 100.0 | 72.1 | 100.0 | NA | NA | |
| Max Spec | RBD | 74.4 | 100.0 | 64.0 | 100.0 | 41.9 | 100.0 |
| S trimer | 84.9 | 100.0 | 84.9 | 100.0 | NA | NA | |
| N | 83.7 | 100.0 | 81.4 | 100.0 | NA | NA | |
| Youden | RBD | 96.5 | 93.7 | 97.7 | 97.9 | 93.0 | 93.7 |
| S trimer | 84.9 | 99.0 | 84.9 | 99.0 | NA | NA | |
| N | 89.5 | 94.8 | 94.2 | 92.7 | NA | NA | |
Abbreviations: Ig, immunoglobulin; Max Spec, maximum specificity; N, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid protein; NA, not applicable; RBD, SARS-CoV-2 receptor-binding domain; S trimer; SARS-CoV-2 spike trimer; SD, standard deviation.
The 3SD threshold was determined by calculating the mean + 3 SDs for negative controls; the Max Spec threshold, by setting the cutoff at the highest value of the negative controls for each antigen-isotype combination; and the Youden threshold, by determining the maximum Youden index on the ROC curve.