TABLE 3.
Per-patient smear results by different reference methods
| Reference standard and smear method | No. of patients (n = 212) with indicated result in reference standard test that were positive by indicated smear method |
Sensitivity [no. positive, % (95% CI)]a | P valueb | Specificity [no. negative, % (95% CI)]c | P value | PPVd ([no. positive/total no. (%)] | NPVe ([no. negative/total no. (%)] | ||
|---|---|---|---|---|---|---|---|---|---|
|
M. tuberculosis |
Contaminated (culture) or invalid/error (Xpert) | ||||||||
| Not detected | Detected | ||||||||
| Culturef | 134 | 76 | 2 | ||||||
| Direct | 3 | 51 | 0 | 51, 67.1 (55.4–77.5) | 0.0004 | 131, 97.8 (93.6–99.5) | 0.625 | 51/54 (94.4) | 131/156 (84.0) |
| Concentrated | 7 | 52 | 0 | 52, 68.4 (56.8–78.6) | 0.0002 | 127, 94.8 (89.5–97.9) | 0.031 | 52/59 (88.1) | 127/151 (84.1) |
| SMF | 1 | 39 | 0 | 39, 51.3 (39.6–63.0) | 133, 99.3 (95.9–100) | 39/40 (97.5) | 133/170 (78.2) | ||
| Xpert test | 142 | 70 | 0 | ||||||
| Direct | 4 | 50 | 0 | 50, 71.4 (59.4–81.6) | 0.0004 | 138, 97.2 (92.9–99.2) | 0.625 | 50/54 (92.6) | 138/158 (87.3) |
| Concentrated | 8 | 51 | 0 | 51, 72.9 (60.9–82.8) | 0.0002 | 134, 94.4 (89.2–97.5) | 0.031 | 51/59 (86.4) | 134/153 (87.6) |
| SMF | 2 | 38 | 0 | 38, 54.3 (41.9–66.3) | 140, 98.6 (95.0–99.8) | 38/40 (95.0) | 140/172 (81.4) | ||
a
Sensitivity: for culture, n = 76, and for Xpert test, n = 70.
b
P values were calculated using McNemar's test. All comparisons are against SMF smear method.
c
Specificity: for culture, n = 134, and for Xpert test, n = 142.
d
PPV, positive predictive value.
e
NPV, negative predictive value.
f
Includes any culture-positive (MGIT or Lowenstein-Jensen medium) result for the same patient.