Humans have cells in their blood stream called endothelial progenitor cells or EPCs. These are thought to be important in keeping blood vessels healthy. People with chronic kidney disease (CKD) have low numbers of these cells. People with cardiovascular (heart and blood vessel) disease also have low numbers. Patients with CKD have more cardiovascular disease then any other group.Erythropoietin is a hormone made by the kidneys. It is essential for making red blood cells and also activates EPCs. It is low in people with kidney disease.