After exclusion of the phospholipids the five metabolites N-palmitoyl glutamic acid, glycocholic acid, hexanoylcarnitine, chenodeoxyglycocholate and PAGN remained. They were used to build a refined validation cohort OPLS-DA model (Fig. 5a, b) to evaluate their discriminatory power in the absence of phospholipids. The predictive ability of the refined model as indicated by the Q2(cum) value was 0.513, i.e. approximately 50% of samples were correctly classified, and the R2X(cum) value was 0.736. The statistical significance of the model as indicated by cross-validated ANOVA was p = 8.2E−07.