To the Editors:
We read with interest the article by Rosias et al. 1 in a recent issue of the European Respiratory Journal. The authors attempted to validate a number of assays using exhaled breath condensate. The values described by Rosias et al. 1 were very similar to those reported by many laboratories, but our interpretation of the data is different. Our experience in validating similar assays in this medium suggests that measuring mediators at these low concentrations is problematic and, as such, we have the following concerns with the article which other researchers need to be aware of.
First, Rosias et al. 1 based coefficient of variation (CV) on a mean of spiked samples, where the spike was far in excess of the measured values. The CVs given were based upon the sample plus spike, rather than the sample alone. In the majority of assays, the working range …