Table 2.
Sensitivity (95%CI) of the VITROS SARS-CoV-2 Antigen test in SARS-CoV-2 RNA-positive samples from the retrospective and prospective cohorts, according to the number of days after symptom onset and the viral load assessed by the cycle threshold value (Ct) in RT-PCR.
| Retrospective cohort(N = 147) | Prospective cohort(N = 145) | |||
|---|---|---|---|---|
| Days from symptom onset | ||||
| N Ag+/ N PCR+ | Sensitivity (95% CI) | N Ag+/ N PCR+ | Sensitivity (95% CI) | |
| Days ≤3 | 18/25 | 72.0% (50.6–87.9) | 40/48 | 83.3% (69.8–92.5) |
| Days 4–7 | 17/22 | 77.3% (54.6–92.2) | 8/8 | 100% (63.1–100) |
| Days 8–11 | 12/20 | 60.0% (36.1–80.9) | 6/8 | 75.0% (34.9–96.8) |
| Days ≥12 | 2/4 | 50.0% (6.8–86.1) | 3/12 | 25.0% (5.5–57.2) |
| Asymptomatic | 0/1 | 0.0% (0.0 −97.5) | 30/43 | 69.8% (53.9–82.8) |
| Unknown | 64/75 | 85.3% (75.3–92.4) | 15/25 | 60% (38.7–79.8) |
| Ct value category | ||||
| Ct ≤20 | 20/21 | 95.2% (76.2–99.9) | 23/23 | 100% (85.2–100) |
| Ct 21–25 | 46/46 | 100% (92.3–100.0) | 37/38 | 97.4% (86.2–99.9) |
| Ct 26–30 | 30/32 | 93.8% (79.2–99.2) | 24/24 | 100% (85.8–100) |
| Ct 31–35 | 15/35 | 42.9% (26.3–60.6) | 16/22 | 72.7% (49.8–89.3) |
| Ct 36–39 | 2/13 | 15.4% (1.9–45.4) | 1/6 | 16.7% (0.4–64.1) |
| Ct ≤30 | 96/99 | 97.0% (91.4–99.4) | 84/85 | 98.8% (93.6–100.0) |
| Ct ≤33 | 105/113 | 92.9% (86.5–96.9) | 95/100 | 95.0% (88.7–98.4) |
| Ct ≤35 | 111/134 | 82.8% (75.9–88.8) | 100/107 | 93.5% (87.0–97.3) |