Biomarkers SDF-1α analysis and the analysis of biomarkers associated with the prevalence of circulating EPCs will be measured using sandwich ELISA and multi-array ELISA technology in-line with manufacturer protocols. Analysis of endogenous DPP4 will be assayed using a commercial colorimetric assay; again manufacturer protocols will be followed. Biomarker and DPP4 analysis will be carried out in one batch on stored sodium heparin plasma samples.