Table 2. Performance characteristics of BIOCREDIT COVID-19 antigen test in all participants and in different subgroups.
| Subgroups | Number | Sensitivity | Specificity | Accuracy |
|---|---|---|---|---|
| All participants | 200 | 34.4% | 98.7% | 58.5% |
| According to patients' symptoms | ||||
| Asymptomatic | 5 | 0 | 100% | 60% |
| Fever alone | 14 | 40% | 100% | 57.1% |
| Respiratory symptoms alone | 100 | 34.3% | 97% | 55% |
| GI symptoms alone | 15 | 25% | 100.0% | 80% |
| Both respiratory and GI symptoms | 66 | 35.7% | 100.0% | 59.1% |
| According to severity | ||||
| Severe | 106 | 56.2% | 97% | 68.9% |
| Nonsevere | 94 | 3.8% | 100% | 46.8% |
| According to viral load a | ||||
| High viral load | 16 | 100% | – | 100% |
| Low viral load | 184 | 24.8% | 98.7% | 54.9% |
| ≥ 1000 copies /µL b | 57 | 75.4% | – | 75.4% |
| < 1000 copies /µL | 143 | 0 | 98.7% | 51.7% |
| According to CRP level | ||||
| ≤ 31.6 mg/L c | 80 | 17.1% | 100.0% | 63.75% |
| >31.6 mg/L | 120 | 41.1% | 96.75 | 55% |
| According to NLR | ||||
| ≤ 3.57 d | 71 | 25% | 100% | 78.9% |
| > 3.57 | 129 | 36.2% | 95.8% | 47.3% |
Abbreviations: COVID-19, coronavirus disease 2019; CRP, C-reactive protein; GI, gastrointestinal; NLR, neutrophil to lymphocyte ratio; PCR-Ct, polymerase chain reaction cycle threshold; ROC, receiver operating characteristics; WHO, World Health Organization.
a
High viral load: if PCR-Ct value ≤ 18 (equivalent to viral copies/ µ L > 158865.647); low viral load: if PCR negative or PCR positive with Ct value > 18 (equivalent to viral copies/ µ L ≤ 158865.647).
b
Contagious patients as assumed by the WHO. 9
c
Cutoff value determined by ROC curve at which CRP could be used as a predictor of COVID-19 infection.
d
Cutoff value determined by ROC curve at which NLR could be used as a predictor of COVID-19 infection.