To the Editors:
We read with great interest the letter by Liu et al. 1 and fully agree that exhaled breath condensate (EBC) collection devices significantly affect EBC biomarker levels, and that absolute values from different devices are not directly comparable 1, 2. We also agree that one single (currently available) collection device may not be ideal for all applications and that, in future studies, each marker may need to be tested by a variety of devices in order to determine the optimal collection apparatus 2. In our opinion, some additional considerations of EBC methodology should be made. We believe that these may change our current view on the variability associated with the measurement of exhaled markers in EBC. In turn, this altered consciousness may provide a tentative way out of current methodological controversies and, by consequence, it may offer new perspectives towards the standardisation of EBC methodology 3.
First, the levels of nitrogen oxides and total protein measured by Liu et al. 1 in EBC were expressed as nmol or μg “per …