Fig. 2.

Receiver operating characteristics (ROC) curve of malondialdehyde (MDA) and 3-nitrotyrosine (3-NT) in exhaled breath condensate (EBC) for the diagnostic discrimination of chronic obstructive pulmonary disease. Area under the curve of the ROC curve of EBC MDA and 3-NT were 0.67 [95% confidence interval (CI): 0.56–0.79; p = 0.004] and 0.62 (95% CI: 0.50–0.74, p = 0.058), respectively. The optimal cutoff values were 5.34 nM (64.9% sensitivity and 64.2% specificity) and 5.58 nM (62.2% sensitivity and 62.3% specificity), respectively.