TABLE 6.
Positive and negative predictive values of the IgG test at different levels of seroprevalence
| Prevalence (%) (n = 100,000) | Sensitivitya (%) | Specificityb (%) | No. of positive tests/no. of COVID+ samplesc | No. of positive tests/no. of COVID− samplesd | PPVe (%) | NPVf (%) |
|---|---|---|---|---|---|---|
| 1 | 91 | 99 | 860/1,000 | 990/99,000 | 48 | 99.9 |
| 10 | 91 | 99 | 8,600/10,000 | 900/90,000 | 91 | 99 |
| 20 | 91 | 99 | 17,200/20,000 | 800/80,000 | 96 | 98 |
| 30 | 91 | 99 | 27,300/30,000 | 700/70,000 | 98 | 96 |
a
Sensitivity at a cutoff of 0.9.
b
Specificity at a cutoff of 0.9.
c
Calculated number of positive tests in the group of true-positive samples.
d
Calculated number of positive tests in the group of true-negative samples.
e
PPV, positive predictive value (likelihood that a positive test predicts a true positive).
f
NPV, negative predictive value (likelihood that a negative test predicts a true negative).