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Table 3 Xpert MTB/RIF Assay performance vs. MTB culture stratified by specimen collection method and specimen type

From: Performance of the G4 Xpert® MTB/RIF assay for the detection of Mycobacterium tuberculosis and rifampin resistance: a retrospective case-control study of analytical and clinical samples from high- and low-tuberculosis prevalence settings

  AFB Smear-positive subjects AFB Smear-negative subjects All samples
Specimen Collection Methoda
Expectorated Sputum (n = 535)
 Sensitivity 99.6% (271/272)b 79.0% (75/95)c 94.3% (346/367)d
95% CI: 97.9 – 99.9% 95% CI: 69.7 – 85.9% 95% CI: 91.4 – 96.2%
 Specificity    97.6% (164/168)b
95% CI: 94.0 – 99.1%
Induced Sputum (n = 234)  
 Sensitivity 100% (15/15)b 40.0% (4/10)c 76% (19/25)d
95% CI: 79.6 – 100% 95% CI: 16.8 – 68.7% 95% CI: 56.6 – 85.5%
 Specificity    99.0% (207/209)b
95% CI: 96.6 – 99.7%
Specimen Type
Raw Sputum (n = 606)
 Sensitivity 99.7% (285/286)b 79.4% (77/97)e 94.5% (362/383)b
95% CI: 98.0 – 99.9% 95% CI: 70.3 – 86.2% 95% CI: 91.8% - 96.4%
 Specificity    97.8% (218/223)b
95% CI: 94.9 – 99.0%
Concentrated Sputum Sediment (n = 490)
 Sensitivity 100% (65/65)b 60.0% (12/20)e 90.6% (77/85)b
95% CI: 94.4 – 100% 95% CI: 38.7 – 78.1% 95% CI: 82.5% - 95.2%
 Specificity    99.3% (402/405)b
95% CI: 97.8 – 99.7%
  1. aCollection method for 327 specimens was unknown
  2. bp-value for difference > 0.1
  3. cp-value for difference = 0.014
  4. dp-value for difference = 0.004
  5. ep-value for difference = 0.084
  6. AFB acid fast bacteria
  7. 95% CI 95% confidence interval