The discriminative metabolite features selected in the discovery cohort had to meet several criteria to ensure feature quality, regardless of the method of statistical analysis. First, features were manually examined in the raw data. Isotopes, adducts and poor quality features, e.g. low intensity peaks were excluded following manual inspection of peak shape. This removed features judged by the software to be chromatographic peaks, but which they human eye rapidly can assign to be column bleed or similar artefacts. Second, for the univariate part of the analysis workflow, features were re-integrated in the raw data using the Qual and Quan Browsers in Xcalibur version 2.2 (Thermo Scientific) and their statistical significance was confirmed with a Student´s t test (p < 0.05). Third, ion chromatograms of the selected features were extracted from the validation cohort raw data files using the software MassHunter Qual version B.06.00 (Agilent); discovery cohort features that were either not detected or of low quality in the validation cohort were excluded. Fourth, unidentifiable metabolite features were excluded.