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Table 2 Sensitivity and Specificity of Concentrated and Direct Smear, By Reference Outcome

From: Sensitivity of direct versus concentrated sputum smear microscopy in HIV-infected patients suspected of having pulmonary tuberculosis

Concentrated Smear Result Direct Smear Result Total
Gold Standard: Sputum Culture
A. Sensitivity    
  Positive Negative  
Positive 67 (39%) 22 (13%) 89 (52%)
Negative 20 (12%) 61 (36%) 81 (48%)
Total 87 (51%) 83 (49%) 170 (100%)
Sensitivity of Direct Smear = 0.51 (0.43–0.59)
Sensitivity of Concentrated Smear = 0.52 (0.44–0.61)
Sensitivity of Direct + Concentrated Smear = 0.64 (0.56–0.72)a, b
B. Specificity    
  Positive Negative  
Positive 0 (0%) 12 (11%) 12 (11%)
Negative 1 (1%) 96 (88%) 97 (89%)
Total 1 (1%) 108 (99%) 109 (100%)
Specificity of Direct Smear = 0.99 (0.94–1.0)a
Specificity of Concentrated Smear = 0.89 (0.81–0.95)b
Specificity of Direct + Concentrated Smear = 0.88 (0.80–0.94)b
Gold Standard: Sputum Culture + Clinical Criteria
A. Sensitivity    
  Positive Negative  
Positive 67 (34%) 27 (14%) 94 (48%)
Negative 20 (10%) 82 (42%) 102 (52%)
Total 87 (44%) 109 (56%) 196 (100%)
Sensitivity of Direct Smear = 0.44 (0.36–0.52)
Sensitivity of Concentrated Smear = 0.48 (0.40–0.56)
Sensitivity of Direct + Concentrated Smear = 0.58 (0.50–0.66)a, b
B. Specificity    
  Positive Negative  
Positive 0 (0%) 7 (8%) 7 (8%)
Negative 1 (1%) 75 (90%) 76 (92%)
Total 1 (1%) 82 (99%) 83 (100%)
Specificity of Direct Smear = 0.99 (0.93–1.0)
Specificity of Concentrated Smear = 0.92 (0.83–0.97)
Specificity of Direct + Concentrated Smear = 0.90 (0.81–0.96)b
  1. ap < 0.05 for comparison with concentrated smear alone
  2. bp < 0.05 for comparison with direct smear alone