Table 3.
Accuracy of Cycle Threshold Values for Predicting Xpert MTB/RIF False Positivity in New and Retreatment Patients
| Test Use | Suggested CT
Cut-point |
Sensitivity, % (95% CI) |
Specificity, % (95% CI) |
PPV, % (95% CI) |
NPV, % (95% CI) |
Positive LR (95% CI) |
Negative LR (95% CI) |
|---|---|---|---|---|---|---|---|
| New patients (n = 461) | |||||||
| Rule-in | >32.19 | 3 (2–4) | 95 (92–97) | 34 (19–.54) | 93 (90–95) | 5.51 (2.87–10.60) | 0.76 (.63–.92) |
| Rule-out | >14.22 | 95 (82–99) | 6 (4–9) | 9 (6–12) | 93 (76–99) | 1.02 (.94–1.09) | 0.78 (.19–3.22) |
| Youden indexa | >27.08 | 55 (39–70) | 80 (76–84) | 21 (14–30) | 95 (92–97) | 2.79 (1.99–3.92) | 0.56 (.40–.79) |
| Retreatment patients (n = 321) | |||||||
| Rule-in | >30.56 | 27 (15–42) | 95 (91–97) | 46 (27–66) | 89 (85–92) | 5.26 (2.60–10.63) | 0.77 (.65–.92) |
| Rule-out | >26.80 | 95 (84–99) | 36 (30–42) | 20 (15–26) | 98 (92–100) | 1.39 (1.33–1.66) | 0.12 (.03–.49) |
| Youden indexa | >28.36 | 64 (49–78) | 90 (86–93) | 52 (38–65) | 94 (90–96) | 6.59 (4.33–10.01) | 0.39 (.27–.58) |
Abbreviations: CI, confidence interval; CT, cycle threshold; LR, likelihood ratio; NPV, negative predictive value; PPV, positive predictive value.
a Defined as the best compromise between sensitivity and specificity assuming equal weighting [24].