Table 3.
Performance characteristics of PCR at different parasite densities relative to expert laboratory microscopy for active surveillance for Plasmodium falciparum and Plasmodium vivax.a
| Trophozoites/μl (total positive) | Sensitivity (95% CI) | Specificity (95% CI) | Positive Predictive Value (95% CI) | Negative Predictive Value (95% CI) | Accuracy | J Index |
| P. falciparum | ||||||
| >5000/μl (14) | 100.0% (73.2–100.0) | 97.7% (97.4–98.0) | 6.7% (3.9–11.3) | 100.0% (99.9–100.0) | 98% | 0.98 |
| >1000/μl (36) | 97.2% (83.8–99.9) | 98.0% (97.7–98.3) | 16.8% (12.1–22.8) | 100.0% (99.9–100.0) | 98% | 0.95 |
| >500/μl (47) | 95.7% (84.3–99.3) | 98.1% (97.8–98.4) | 21.6% (16.4–28.0) | 100.0% (99.9–100.0) | 98% | 0.94 |
| >100/μl (151) | 58.3% (50.0–66.2) | 98.6% (98.3–98.8) | 42.3% (35.6–49.3) | 99.2% (99.0–99.4) | 98% | 0.57 |
| >1/μl (267) | 41.6% (35.7–47.8) | 98.8% (98.6–99.0) | 53.6% (46.6–60.5) | 98.1% (97.8–98.4) | 97% | 0.40 |
| P. vivax | ||||||
| >5000/μl (4) | 100.0% (39.6–100.0) | 95.5% (95.0–95.9) | 1.0% (0.3–2.8) | 100.0% (99.9–100.0) | 95% | 0.95 |
| >1000/μl (15) | 100.0% (74.7–100.0) | 95.6% (95.2–96.0) | 3.8% (2.2–6.1) | 100.0% (99.9–100.0) | 96% | 0.96 |
| >500/μl (20) | 100.0% (80.0–100.0) | 95.7% (95.2–96.1) | 5.1% (3.2–7.9) | 100.0% (99.9–100.0) | 96% | 0.96 |
| >100/μl (96) | 71.9% (61.6–80.3) | 96.2% (95.8–96.6) | 17.6% (14.1–21.9) | 99.7% (99.5–99.8) | 96% | 0.68 |
| >1/μl (387) | 35.9% (31.2–40.9) | 96.9% (96.5–97.3) | 35.8% (31.1–40.8) | 97.0% (96.5–97.3) | 94% | 0.33 |
a For this analysis we assume that microscopy is the gold standard (i.e., always correct).