The effect of gas standardisation on exhaled breath condensate pH.

We have read with interest the American Thoracic Society/ European Respiratory Society Task Force document on exhaled breath condensate (EBC) [1]. EBC pH is emerging as a potential biomarker in respiratory disease. Gas standardisation (or deaeration) of EBC with argon is commonly performed to remove carbon dioxide prior to pH measurement [2–4]. It has been argued that CO2 is unwelcome ‘‘noise’’ in the sample and, although the completeness of CO2 removal has not been confirmed, gas-standardised EBC pH is stable and provides reproducible measurements [3, 4]. However, some authors regard CO2 as a relevant component of EBC and have measured pH without gas standardisation [5, 6]. These variations in methodology make comparison between studies difficult.