Effects of reduced dialysate calcium on calcium-phosphorus product and bone metabolism in hemodialysis patients.

BACKGROUND

The safety of using reduced calcium dialysate (RDC) in hemodialysis (HD) patients is controversial due to related changes in bone metabolism. In the present study we investigated whether an 18-month treatment period with RDC may induce significant changes in calcium-phosphorus product (CaxP), bone metabolism, and components of the insulin-like growth factor (IGF) system in HD patients.

STUDY DESIGN

In this prospective study, 13 HD patients with biochemical signs of diminished or low-normal bone turnover and high CaxP due to high serum calcium level were treated by lowering dialysate calcium from 3.5 to 2.5 mEq/l for 18 months. By specific immunometric assays, serum levels of intact parathyroid hormone (PTH), bone alkaline phosphatase (B-ALP), pyridinoline (PYR), desoxypyridinoline (D-PYR), 25-OH-vitamin D(3) (25-vit D(3)), 1,25-(OH)(2)-vitamin D(3) (1,25-vit D(3)), free IGF-I, IGF-II, and IGF-binding protein (IGFBP)-1 to -6 were measured.

RESULTS

CaxP decreased significantly from 5.62 (baseline) to 3.95 mmol(2)/l(2) (at 18 months), whereas PTH increased from 81 +/- 57 pg/ml at baseline to 236 +/- 188 at 12 months (p < 0.01), remaining in this range thereafter. Parameters of bone resorption (PYR) as well as formation (B-ALP) significantly increased during RDC, with peak levels after 12 months. Despite increasing doses of oral alfacalcidol, levels of 25-vit D(3) and 1,25-vit D(3) subsequently declined during RDC. In parallel with the changes in bone markers, free IGF-I levels decreased (baseline: 1.9 +/- 0.9 ng/ml, after 18 months: 1.1 +/- 0.7; p < 0.01). The decline of free IGF-I correlated with decreasing levels of IGFBP-3 and increasing levels of IGFBP-1/-4.

CONCLUSION

The treatment with RDC effectively lowered CaxP and stimulated bone formation and resorption. The different changes in bone markers and IGF system components mirror the complex effects on bone metabolism.