Discovery of\nHypoxanthine and Inosine as Robust Biomarkers\nfor Predicting the Preanalytical Quality of Human Plasma and Serum\nfor Metabolomics

In cold human blood, the anomalous dynamics of adenosine\ntriphosphate\n(ATP) result in the progressive accumulation of adenosine diphosphate\n(ADP), adenosine monophosphate (AMP), inosine monophosphate (IMP),\ninosine, and hypoxanthine. While the ATP, ADP, AMP, and IMP are confined\nto red blood cells (RBCs), inosine and hypoxanthine are excreted into\nplasma/serum. The plasma/serum levels of inosine and hypoxanthine\ndepend on the temperature of blood and the plasma/serum contact time\nwith the RBCs, and hence they represent robust biomarkers for evaluating\nthe preanalytical quality of plasma/serum. These biomarkers are highly\nspecific since they are generally absent or at very low levels in\nfresh plasma/serum and are highly sensitive since they are derived\nfrom ATP, one of the most abundant metabolites in blood. Further,\nwhether blood was kept at room temperature or on ice could be predicted\nbased on inosine levels. An analysis of >2000 plasma/serum samples\nprocessed for metabolomics-centric analyses showed alarmingly high\nlevels of inosine and hypoxanthine. The results highlight the gravity\nof sample quality challenges with high risk of grossly inaccurate\nmeasurements and incorrect study outcomes. The discovery of these\nrobust biomarkers provides new ways to address the longstanding and\nunderappreciated preanalytical sample quality challenges in the blood\nmetabolomics field.