 Ectonucleotide pyrophosphatase/phosphodiesterase (ENPP) may function to raise extracellular PPi.From the standpoint of high energy phosphate accounting, the hydrolysis of ATP to AMP and PPi requires two high-energy phosphates, as to reconstitute AMP into ATP requires two phosphorylation reactions.The plasma concentration of inorganic pyrophosphate has a reference range of 0.58–3.78 µM (95% prediction interval).