Association between Biomarkers of Mineral and Bone Metabolism and Removal of Calcium and Phosphate in Hemodialysis

Abstract

Background: A significant drop of serum phosphate and calcium removal or loading during hemodialysis induce reactions in mineral and bone remodeling that may inversely affect phosphate and calcium removal during dialysis.

Objectives: We aimed to analyze the interdependencies between biomarkers of mineral and bone metabolism and removal of phosphate and calcium during hemodialysis, as this complex relationship is not fully understood.

Methods: Three subsequent hemodialysis sessions during a 1-week treatment cycle with interdialytic periods of 2-2-3 days were monitored in 25 anuric patients. Calcium and phosphate concentrations were measured in serum before, at 1, 2, and 3 h, at the end, and 45 min after each session and in the outlet dialysate every 30 min. Biomarkers associated with mineral and bone metabolism: parathyroid hormone (PTH 1-34 and PTH 1-84), calcitonin, 25(OH)-vitamin D, fetuin-A, osteopontin, osteocalcin 1-43/49, and intact osteocalcin were assayed once in each patient before the midweek hemodialysis session.

Results: Post-dialytic and intra-dialytic serum phosphate of midweek hemodialysis session and phosphate mass removed within 1 week correlated positively with serum PTH (0.40 < rho <0.46, p value <0.05). Higher concentration of serum PTH was associated with an increased level of osteocalcin. Pre-dialytic, post-dialytic, average for treatment time and average weekly concentrations of ionized calcium in serum correlated positively with serum osteocalcin. Serum osteocalcin and osteopontin levels were associated with the masses of total and ionized calcium, respectively, removed during 3 hemodialysis sessions.

Conclusions: During hemodialysis, phosphate removal was associated with serum PTH, whereas calcium kinetics was influenced by serum osteocalcin and osteopontin. These results demonstrate that active processes involving biomarkers of mineral and bone metabolism are affected by the phosphate and calcium kinetics already within 4 h hemodialysis sessions.

Keywords: Bone turnover markers; Hemodialysis; Osteocalcin; Parathyroid hormone; Phosphate and calcium kinetics.