Changes of bone markers during long-term intravenous calcitriol therapy in maintenance dialysis patients

Twenty patients with end-stage renal failure on maintenance hemodialysis were studied for the effect of intravenous 1,25(OH)2 vitamin D3 on biochemical bone markers. Active vitamin D, 1,25(OH)2 vitamin D3, was given intravenously after hemodialysis, 1 microgram thrice weekly. Serum ionized calcium, phosphorus, alkaline phosphatase (AKPase), intact parathyroid hormone (PTH), osteocalcin (bone Gla protein), carboxy terminal propeptide of type I procollagen (PICP), cross-linked telopeptide of type I collagen (ICTP) and beta 2-microglobulin were measured before and after 3 and 6 months of treatment with 1,25(OH)2 vitamin D3. The serum ionized calcium and osteocalcin levels were significantly increased at 3 and 6 months after treatment. The serum beta 2-microglobulin level were also increased 6 months after treatment, whereas the serum levels of AKPase and intact PTH decreased after treatment. However, the serum levels of phosphorus, PICP and ICTP did not change significantly after treatment. The decreased levels of serum AKPase and intact PTH suggest reduced bone resorption. Increases of serum osteocalcin levels were caused by stimulation of the osteoblast by 1,25(OH)2 vitamin D3, baseline 20.6 +/- 12.5 micrograms/l, and 36.1 +/- 34.0 and 31.0 +/- 24.6 micrograms/l at 3 and 6 months, respectively (p < 0.01). The lower osteocalcin level at 6 rather than at 3 months may imply reduced bone resorption and/or increased bone mineralization. The meaning of the increase of serum beta 2-microglobulin in uremic patients after calcitriol treatment is unclear. It may indicate reduced deposition and is masked by increased bone resorption from secondary or tertiary hyperparathyroidism. This study did not validate PICP and ICTP measurements as bone markers in uremic patients.