Relative levels of metabolites belonging to six different metabolic systems based on FI-MS/MS analysis. A, 36-carbon long-chain FA system; B, PlsEtn system; C, lysoPC system; D, SM system; E, PtdCho system; F, PtdEtn system. Error bars represent ±1 SEM. G, ROC curves based on the metabolites from four of the metabolic systems with the lowest p-values (shown by the horizontal brackets in A, C, D and E). AUCs are shown with 95% CI. See Additional file 1 for parent-daughter transitions.