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Table 2 Fluorescence smear microscopy, GeneXpert MTB MTB/RIF® and Loopamp MTBC Detection Kit® performance

From: Performance and impact of GeneXpert MTB/RIF® and Loopamp MTBC Detection Kit® assays on tuberculosis case detection in Madagascar

Diagnosis assay TP TN FP FN Sensitivity Specificity PPV NPV
n n n n % (95% CI) % (95% CI) % (95% CI) % (95% CI)
Fluorescence smear microscopy
 Total (n = 514) 148 310 3 53 73.6 (67.1–79.3) 99.0 (97.1–99.8) 98.0 (94.1–99.6) 85.4 (81.4–88.7)
GeneXpert MTB/RIF®
 Smear negative (n = 361) 29 300 8 24 54.7 (41.4–67.4) 97.4 (94.9–98.8) 78.4 (62.6–88.9) 92.6 (89.2–95.0)
 Smear positive (n = 148) 145 0 0 3 98.0 (93.9–99.6) N/A 100.0 (96.9–100.0) N/A
 Total (n = 509) 174 300 8 27 86.6 (81.1–90.7) 97.4 (94.9–98.8) 95.6 (91.4–97.9) 91.7 (88.2–94.3)
Loopamp MTBC Detection Kit®
 Smear negative (n = 369) 29 311 5 24 54.7 (41.4–67.4) 98.4 (96.2–99.4) 85.3 (69.4–94.0) 92.8 (89.5–95.2)
 Smear positive (n = 148) 141 0 0 7 95.3 (90.4–97.9) N/A 100.0 (96.8–100.0) N/A
 Total (n = 517) 170 311 5 31 84.6 (78.9–89.0) 98.4 (96.2–99.4) 97.1 (93.3–99.0) 90.9 (87.4–93.6)
  1. CI confidence interval, FN false negative, FP false positive, N/A not applicable, MTB(C) Mycobacterium tuberculosis complex, NPV negative predictive value, PPV positive predictive value, RIF rifampicin, TN true negative, TP true positive