Background
Methods
Setting
VL platforms
Study sample and procedures
Statistical analysis
Results
Baseline characteristics
Both facilities combined | Nhlangano (LAB-1)a | Lobamba (LAB-2)a | p-value | |
---|---|---|---|---|
Total | 364 | 198 (54.4) | 166 (45.4) | |
Age; median (IQR), years | 36 (30–44.5) | 39 (33–48) | 32.5 (27–39) | < 0.01 |
Gender and pregnancy status (missing = 7) | < 0.01 | |||
Men | 111 (31.1) | 64 (32.5) | 47 (29.4) | |
Non-pregnant women | 231 (64.7) | 132 (67.0) | 99 (61.9) | |
Pregnant women | 15 (4.2) | 1 (0.5) | 14 (8.8) | |
Reason for VL test | < 0.01 | |||
Pre-ART | 59 (16.2) | 4 (2.0) | 55 (33.1) | |
ART | 305 (83.8) | 194 (98.0) | 111 (66.9) | |
Time on ART; median (IQR), years | 5.0 (2.0–7.5) | 6.2 (3.3–8.3) | 2.9 (1.8–5.4) | < 0.01 |
VL values on the reference method; log10 copies/mL | < 0.01 | |||
< 1.3 | 236 (64.8) | 150 (75.8) | 86 (51.8) | |
1.3–< 3.0 | 58 (15.9) | 37 (18.7) | 21 (12.7) | |
3.0–< 4.0 | 17 (4.7) | 5 (2.5) | 12 (7.2) | |
≥ 4.0 | 53 (14.6) | 6 (3.0) | 47 (28.3) |
Results of VL quantification using the reference method
Correlation and agreement
Diagnostic accuracy
At 2.62 log10 copies/mL | At 3.0 log10 copies/mL | |||||
---|---|---|---|---|---|---|
LAB-1 (n = 198) | LAB-2 (n = 166) | Combined (n = 364) | LAB-1 (n = 198) | LAB-2 (n = 166) | Combined (n = 364) | |
Sensitivity % (95% CI) | 92.3 (64.0–99.8) | 84.4 (73.1–92.2) | 85.7 (75.9–92.6) | 100 (71.5–100) | 86.4 (75.0–94.0) | 88.6 (78.7–94.9) |
Specificity % (95% CI) | 96.2 (92.4–98.5) | 99.0 (94.7–100) | 97.2 (94.6–98.8) | 97.9 (94.6–99.4) | 99.1 (94.9–100.0) | 98.3 (96.1–99.4) |
ROC area % (95% CI) | 0.94 (0.87–1.00) | 0.92 (0.87–0.96) | 0.92 (0.87–0.96) | 0.99 (0.98–1.00) | 0.93 (0.88–0.97) | 0.93 (0.90–0.97) |
PPV (at 10%)a % (95% CI) | 73.1 (56.3–85.1) | 90.5 (57.6–98.5) | 77.4 (63.2–87.2) | 83.9 (66.3–93.2) | 91.1 (59.3–98.6) | 85.3 (70.7–93.3) |
NPV (at 10%)a % (95% CI) | 99.1 (94.5–99.9) | 98.3 (97.0–99.0) | 98.4 (97.3–99.1) | 100 (93.3–100) | 98.5 (97.2–99.2) | 98.7 (97.6–99.3) |
PPV (at 20%)a % (95% CI) | 85.9 (74.4–92.8) | 95.6 (75.3–99.3) | 88.5 (79.4–93.9) | 92.1 (81.6–96.9) | 95.9 (76.6–99.4) | 92.9 (84.5–96.9) |
NPV (at 20%)a % (95% CI) | 98.0 (88.4–99.7) | 96.2 (93.5–97.8) | 96.5 (94.0–97.9) | 100 (86.1–99.9) | 96.7 (93.9–98.2) | 97.2 (94.7–98.5) |
Misclassification
Lab | Reason for VL testing | Time to freezing (hours)a | VL results during first round of VL quantification | VL results after re-quantification | |||||
---|---|---|---|---|---|---|---|---|---|
Reference method (log10 copies/mL-l) | Biocentric platform (log10 copies/mL-l) | Misclassification | Biocentric platform (log10 copies/mL-l) | Misclassification | |||||
2.62 log10 copies/mL | 3.0 log10 copies/mL | 2.62 log10 copies/mL | 3.0 log10 copies/mL | ||||||
Lab-1 | ART | 2.7 | 0 | 3.14 | upward | upward | * | * | * |
Lab-1 | ART | 3.8 | 0 | 2.65 | upward | CON | 0 | CON | CON |
Lab-1 | ART | 1.1 | 0 | 3.03 | upward | upward | 0 | CON | CON |
Lab-1 | ART | 0.9 | 0 | 4.00 | upward | upward | 0 | CON | CON |
Lab-1 | ART | 0.5 | 0 | 2.70 | upward | CON | * | * | * |
Lab-1 | ART | 0.3 | 2.25 | 2.92 | upward | CON | * | * | * |
Lab-1 | ART | 1.5 | 2.37 | 2.68 | upward | CON | 0 | CON | CON |
Lab-2 | Pre-ART | 2.2 | 2.48 | 3.34 | upward | upward | 2.78 | upward | CON |
Lab-2 | ART | 4.4 | 2.72 | 0 | downward | CON | 0 | downward | CON |
Lab-1 | ART | 1.6 | 2.73 | 0 | downward | CON | * | * | * |
Lab-1 | ART | 2.4 | 2.78 | 3.03 | CON | upward | * | * | * |
Lab-2 | Pre-ART | 2.6 | 2.84 | 0 | downward | CON | 2.84 | CON | CON |
Lab-2 | Pre-ART | 1.2 | 2.90 | 0 | downward | CON | 0 | downward | CON |
Lab-2 | Pre-ART | 1.4 | 2.91 | 0 | downward | CON | 3.00 (999b) | CON | upwardb |
Lab-2 | Pre-ART | 1 | 3.13 | 0 | downward | downward | 0 | downward | downward |
Lab-2 | ART | 2.6 | 3.21 | 0 | downward | downward | 3.51 | CON | CON |
Lab-2 | Pre-ART | 3 | 3.31 | 0 | downward | downward | 0 | downward | downward |
Lab-2 | Pre-ART | 3.2 | 3.40 | 2.96 | CON | downward | 3.84 | CON | CON |
Lab-2 | Pre-ART | 4.7 | 3.63 | 2.89 | CON | downward | 3.60 | CON | CON |
Lab-2 | Pre-ART | 4.1 | 3.77 | 0 | downward | downward | 3.06 | CON | CON |
Lab-2 | ART | 0.3 | 3.82 | 0 | downward | downward | 3.95 | CON | CON |
Lab-2 | Pre-ART | 2.5 | 4.17 | 0 | downward | downward | 4.29 | CON | CON |
Re-quantification of discordant VL values
At 2.62 log10 copies/mL (n = 364) | At 3.0 log10 copies/mL (n = 364) | |
---|---|---|
Sensitivity % (95% CI) | 93.5 (85.5–97.9) | 97.1 (90.1–99.7) |
Specificity % (95% CI) | 98.6 (96.5–99.6) | 99.0 (97.0–99.8) |
ROC area % (95% CI) | 0.96 (0.93–0.99) | 0.98 (0.96–1.0) |
PPV (at 10%)a % (95% CI) | 88.2 (73.8–95.2) | 91.4 (77.4–97.0) |
NPV (at 10%)a % (95% CI) | 99.3 (98.3–99.7) | 99.7 (98.8–99.9) |
PPV (at 20%)a % (95% CI) | 94.4 (86.4–97.8) | 96.0 (88.5–98.7) |
NPV (at 20%)a % (95% CI) | 98.4 (96.3–99.3) | 99.3 (97.2–99.8) |