Table 1.
The variation of sensitivity and specificity of the in-house antigen ELISA system depending on Ct value and storage condition as compared to RT-qPCR result (n = 339)
| ELISA +/ RT-qPCR + | ELISA -/ RT-qPCR- | Sensitivity (95% CI) |
Specificity (95% CI) |
PPV (95% CI) |
NPV (95% CI) |
|
|---|---|---|---|---|---|---|
| With All Ct Value | ||||||
| Overall | 91/147 | 190/192 | 61.9 (53.5, 69.8) |
99.0 (96.3, 99.9) |
97.8 (92.4, 99.7) |
77.2 (71.5, 82.3) |
| 4°C followed by −80°C | 34/63 | 53/53 | 54.0 (40.9, 66.6) |
100.0 (93.3, 100) |
100 (89.7, 100) |
64.6 (53.3, 74.9) |
| −20°C | 4/9 | 22/22 | 44.4 (13.7, 48) |
100.0 (84.6, 100) |
100 (39.8, 100) |
81.5 (61.9, 93.7) |
| −80°C | 53/75 | 115/117 | 70.7 (59, 80.6) |
98.3 (94, 99.8) |
96.4 (87.5, 99.6) |
83.9 (76.7, 89.7) |
| Ct ≤35 | ||||||
| Overall | 80/115 | 190/192 | 69.6 (60.3, 77.8) |
99.0 (96.3, 99.9) |
97.6 (91.5, 99.7) |
84.4 (79, 88.9) |
| 4°C followed by −80°C | 34/62 | 53/53 | 54.8 (41.7, 67.5) |
100.0 (93.3, 100) |
100 (89.7, 100) |
65.4 (54, 75.5) |
| −20°C | 3/5 | 22/22 | 60.0 (14.7, 94.7) |
100.0 (84.6, 100) |
100 (29.2, 100) |
91.7 (73.0, 99.0) |
| −80°C | 43/48 | 115/117 | 89.6 (77.3, 96.5) |
98.3 (94, 99.8) |
95.6 (84.9, 99.5) |
95.8 (90.5, 98.6) |
| Ct ≤30 | ||||||
| Overall | 49/65 | 190/192 | 75.4 (63.1, 85.2) |
99.0 (96.3, 99.9) |
96.1 (86.5, 99.5) |
92.2 (87.7, 95.5) |
| 4°C followed by −80°C | 22/36 | 53/53 | 61.1 (43.5, 76.9) |
100.0 (93.3, 100) |
100 (84.6, 100) |
79.1 (67.4, 88.1) |
| −20°C | 1/1 | 22/22 | 100.0 (2.5, 100) |
100.0 (84.6, 100) |
100.0 (2.5, 100) |
100.0 (84.6, 100) |
| −80°C | 26/28 | 115/117 | 92.9 (76.5, 99.1) |
98.3 (94, 99.8) |
92.9 (76.5, 99.1) |
98.3 (94, 99.8) |
Note: AUC: Area under curve; 95% CI: 95% Confidence interval. Cohen’s Kappa test was used to evaluate the test agreement.