As in hemodialysis, elevated phosphorus, calcium-phosphorus product raise cardiovascular mortality.
Developed under the National Kidney Foundation’s Kidney Disease Outcomes Quality Initiative (K/DOQI), the guidelines are based predominantly on studies in hemodialysis (HD) patients. Although the guidelines are broadly applied to the PD population, the investigators noted that the relationship between abnormal mineral metabolism and cardiovascular mortality has never been studied in PD patients.
A study led by Marlies Noordzij, MSc, of the University of Amsterdam, compared 586 PD patients with 1,043 HD patients. The median follow-up was 28-29 months, during which 102 PD patients and 271 HD patients were hospitalized for CVD.
The K/DOQI guidelines recommend blood concentrations of calcium in CKD patients between 8.4 and 9.5 mg/dL and phosphorus concentrations between 3.5 and 5.5 mg/dL. Calcium-phosphorus product (Ca × P) should be less than 55 mg2/dL2 and intact parathyroid hormone (iPTH) should range from 150-300 pg/mL.
The risk of cardiovascular mortality in the PD patients did not differ significantly by calcium
level, but it was twofold higher in those with elevated phosphorus and Ca × P compared with those with levels within the target range, the investigators reported in Nephrology Dialysis Transplantation (2006;21:2513-2520). The risk of cardiovascular mortality also did not differ by calcium level in the HD group, but elevated phosphorus and Ca × P each increased the risk by 1.5 times compared with on-target levels, the study showed. In both groups, Noordzij and his colleagues found no significant association between abnormal iPTH levels and cardiovascular morbidity and mortality.
Among HD patients, those with elevated calcium levels had a significantly increased risk of CVD-related hospitalization compared with those with on-target levels, according to the researchers. The risk was not significantly different for patients whose calcium levels were below target, they reported.
“CVD-related mortality risk is increased in PD and in HD patients with elevated plasma phosphorus and Ca × P concentrations,” the authors said.