Table 3

Sensitivity and specificity of nitrogen washout tests as compared with methacholine challenge tests

MCT20*MCT40
SIII baseline
N2SBW
Sensitivity12%10.4%
Specificity90.7%89.1%
Positive likelihood ratio1.300.96
Negative likelihood ratio0.971.01
Accuracy‡86.02%84.4%
LCI
N2MBW
Sensitivity80.4%79.1%
Specificity18.6%18.9%
Positive likelihood ratio0.990.98
Negative likelihood ratio1.051.11
Accuracy‡22.3%22.5%
Scond
N2MBW
Sensitivity21.7%20.9%
Specificity86.1%83.8%
Positive likelihood ratio1.561.29
Negative likelihood ratio0.910.94
Accuracy‡82.2%80%
Sacin
N2MBW
Sensitivity45.7%41.9%
Specificity60.5%62.2%
Positive likelihood ratio1.151.11
Negative likelihood ratio0.900.94
Accuracy‡59.6%60.9%
  • *Sensitivity, specificity, likelihood ratios and accuracy from washout methods calculated as compared with the reference standard MCT20 (methacholine challenge test according to ≥20% fall of FEV1).

  • †Sensitivity, specificity, likelihood ratios and accuracy from washout methods calculated as compared with the reference standard MCT40(positive methacholine challenge test according to fall of ≥40% of specific airway conductance).

  • ‡Disease prevalence of 6%.27

  • FEV1, forced expiratory volume in the first second; MCT, methacholine challenge test; N2MBW, nitrogen multiple breath washout; N2SBW, nitrogen single breath washout; SGeff, specific airway conductance; SIII, slope III from N2SBW.