Table 3.
The sensitivity and specificity of the Rapid SARS-CoV-2 antigen assay according to different viral loads based on Ct (cycle threshold) values
| Rapid SARS-CoV-2 antigen assay | Real-time RT-PCR | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| (Ct < 20) | (Ct 21–30) | (Ct > 30) | |||||||
| Positive | Negative | Total | Positive | Negative | Total | Positive | Negative | Total | |
| Positive | 8 | 3 | 11 | 21 | 3 | 24 | 6 | 3 | 9 |
| Negative | 0 | 1,024 | 1,024 | 21 | 1,024 | 1,045 | 13 | 1,024 | 1,037 |
| Total | 8 | 1,027 | 1,035 | 42 | 1,027 | 1,069 | 19 | 1,027 | 1,046 |
| Sensitivity (95% CI) | 100% (63.06–100.00%) | 50.00% (34.19–65.81%) | 31.58% (12.58–56.55%) | ||||||
| Specificity (95% CI) | 99.71% (99.15–99.94%) | 99.71% (99.15–99.94) | 99.71% (99.15–99.94) | ||||||
CI = confidence interval; Ct = cycle threshold; RT-PCR = reverse-transcriptase polymerase chain reaction; SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2.