Arterial calcifications start at early stages of chronic kidney disease (CKD) and are associated to cardiovascular mortality. Pyrophosphate (PPi) is an endogenous compound, which stops the mineralization process in bones and is expected to act at ectopic sites. In uremic rats, low PPi plasma levels are associated with high calcium content in the aorta and peritoneal administration of PPi blocks this process. People on maintenance dialysis or kidney transplant recipients have low plasma levels of PPi and show high scores of arterial calcification. The purpose is to determine the role of low PPi in the development of arterial calcifications in patients with CKD stage 3 or 4. To that aim, 252 patients with eGFR between 59 et 20 ml/min/1,73 m2 will be recruited and will be examined at baseline and three years later.

Inclusion Criteria:

• eGFR between 59 et 20 ml/min/1,73 m2 twice at three month interval

Exclusion Criteria:

1. kidney transplantation
2. acute inflammatory disease or active cancer