Metabolomics of chronic obstructive pulmonary disease and obstructive sleep apnea syndrome: a comment

We have read with great interest the paper by Za?bek et al. published in Metabolomics, who evaluated the possibility to distinguish the COPD disease from the OSA syndrome using a set of selected metabolites from different biofluids (serum, exhaled breath condensate, urine). The authors also evaluated whether a combination of metabolites present in two or in all biofluids could improve the diagnostic power of the proposed model. The main conclusions of the study are: (a) only ten urine metabolites are required to separate COPD from OSA syndrome; (b) a combination of metabolites from two or three biofluids does not improve the predictiveness of the diagnostic model, and (c) changes in the concentration in the EBC metabolites were not specific enough to correctly predict the COPD or OSAS in individuals. The data reported are of extreme interest considering that OSAS occurs in ca. 10-20 % of COPD patients, and that both conditions share the same comorbidities, making their differentiation quite difficult. For this reason we believe that the clinical profiles of patients (Table 1 in Za?bek et al.) need more details.