Table 4.
Predictive values at cut-off values 0.400 and 0.200
| cut-off 0.400 | cut-off 0.200 | |||||
|---|---|---|---|---|---|---|
| PCR posb | PCR negb | TOTALa | PCR posb | PCR negb | TOTALa | |
| TB pos (n) | 199 | 41 | 240 | 221 | 19 | 240 |
| TB neg (n) | 21 | 2739 | 2760 | 414 | 2346 | 2760 |
| TOTAL (n) | 220 | 2780 | 3000 | 635 | 2365 | 3000 |
| PPVc (%) | 90.4 | 34.8 | ||||
| NPVc (%) | 98.5 | 99.1 | ||||
a Based on the assumption of a mean rate of 8.0% true TB positive specimens and a total number of 3000 specimens in a routine TB laboratory per year, the resulting numbers of TB positive and negative samples were calculated.
b Based on the specificity and sensitivity values found in this study, the numbers of expected PCR positive and negative results among 3000 were calculated. Resulting numerical values were rounded.
c Positive and negative predictive values were deduced from calculated PCR positive and negative results.