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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

From: Comparison of PCR and microscopy for the detection of asymptomatic malaria in a Plasmodium falciparum/vivax endemic area in Thailand

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
  1. a For this analysis we assume that microscopy is the gold standard (i.e., always correct).