AHSG and chronic kidney disease: This includes not only fetuin-A but also osteopontin, which is produced by many tissues and, like fetuin-A, acts as a phosphate binding protein and buffer.32 Furthermore, pyrophosphate (PPi) and magnesium block the chemical reaction underlying the formation of calcium-phosphate crystals.33,34 In CKD, systemic levels of fetuin-A, PPi, and magnesium are reduced,33,35,36 which combined with increasing phosphate concentrations results in high CPP levels (Figure 1).