• Rosalba Accordino, Annalisa Visentin, Anna Bordin, Silvia Ferrazzoni, Emanuela Marian, Federico Rizzato, Cristina Canova, Roberta Venturini, and Piero Maestrelli.
• Department of Environmental Medicine and Public Health, University of Padova, and Department of Laboratory Medicine, Azienda Ospedaliera di Padova, Italy.
• Respir Med. 2008 Mar 1; 102 (3): 377-81.

AbstractExhaled breath condensate (EBC) is being used increasingly to sample airway fluid. EBC pH may be a biomarker of airway inflammation in asthma. In this study, we assessed the long-term reproducibility of EBC pH in asthma. We examined 31 asthmatic patients and eight healthy subjects three times over a 1-year period (winter, autumn and summer). EBC pH was measured after argon deaeration. Repeatability of pH measurements was assessed using intraclass correlation coefficients (ICC) and the limits of agreement (LOA) between seasons were calculated according to Bland-Altman method. No significant differences in EBC pH between seasons were detected in healthy subjects and asthmatic patients. EBC pH showed high repeatability either in healthy subjects (ICC=0.94) or in asthmatics (ICC=0.97). Variability between seasons was greater in asthmatics than in healthy subjects: winter-autumn LOA -0.68/+0.52 and -0.31/+0.31, autumn-summer LOA -0.75/+0.67 and -0.24/+0.15, winter-summer LOA -0.92/+0.67 and -0.34/+0.23 in asthmatic and healthy subjects, respectively. In a subgroup of 11 asthmatics who remained in stable conditions during the study, no substantially different LOA were observed in EBC pH compared with the whole group of asthmatics. Asthmatic smokers (n=10) tended to have lower EBC pH (7.57+/-0.46) than asthmatic non-smokers (n=21) (7.74+/-0.21; p=0.063) and wider LOA. In conclusion, we demonstrated that EBC pH exhibits good repeatability in long-term assessment. EBC pH in asthmatics tended to fluctuate more than in healthy subjects. However, EBC pH variability in asthma was not influenced by changes in clinical status. Rather, we suggest that cigarette smoke may be implicated in EBC pH variability.

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