Table 2. Diagnostic performance of Standard ™ Q COVID-19 Ag test against the RT-qPCR at various Ct categories
Features Subgroup RT-qPCR test RT-qPCR test Sensitivity % (CI) Specificity % (CI) Accuracy % Likelihood ratio
Standard ™ Q COVID-19 Ag test
Positive (n = 69) Negative (n = 14)
All
Ct values
Positive (n = 59)
54
5
78.2 (0.67-0.86) 64.2 (0.38-0.83)
75.9
2.1
Negative (n = 24)
15
9
Subgroups of RT-qPCR positive patients* Strongly positive (< 29)
Positive
28
28
96.5 (0.83-0.99) 44 (0.31-0.57)
63.2
1.7
Negative 1 22
Moderately positive (29-36)
Positive
21
38
72.4 (0.54-0.85) 29.6 (0.19-0.42)
44.5
1
Negative 8 16
Weakly positive (37-39)
Positive
5
54
45.4 (0.21-0.71) 23.9 (0.15-0.35)
26.8
0.59
Negative 6 17