Effect of Dialysate Calcium Concentrations on Parathyroid Hormone and Calcium Balance During a Single Dialysis Session Using Bicarbonate Hemodialysis: A Crossover Clinical Trial

Background: In bicarbonate-based hemodialysis, dialysate total calcium (tCa) concentration may have effects on mineral metabolism. Study Design: Randomized crossover trial of 3 dialysate tCa concentrations (2.5, 2.75, and 3.0 mEq/L). Setting & Participants: 22 stable anuric uremic patients underwent three 4-hour bicarbonate hemodialysis sessions with the 3 different dialysate tCa concentrations using a single-pass batch dialysis system. Outcomes: Hourly measurements of plasma water ionized calcium (iCa) and plasma parathyroid hormone (PTH) concentrations. tCa mass balances were measured from the dialysate side. Results: Hourly plasma water iCa concentrations were higher with a dialysate tCa concentration of 3.0 compared with 2.75 and 2.5 mEq/L (P < 0.05), as were iCa concentrations at the end of dialysis sessions (2.66 +/- 0.1, 2.56 +/- 0.12, and 2.4 +/- 0.08 mEq/L, respectively; P < 0.001). Mean tCa mass balance values (diffusion gradient from the dialysate to the patient) were positive with all dialysate tCa concentrations and increased progressively with dialysate tCa concentration (75 +/- 122, 182 +/- 125, and 293 +/- 228 mg, respectively; P < 0.001). Plasma PTH levels increased during dialysis using dialysate tCa concentration of 2.5 mEq/L (mean increase, 225 +/- 312 pg/mL) and decreased with dialysate tCa concentrations of 2.75 and 3.0 mEq/L (mean decreases, 68 +/- 325 and 99 +/- 432 pg/mL, respectively). Limitations: Small sample size and lack of measurement of total-body calcium mass balances. Conclusions: A dialysate tCa concentration of 2.75 mEq/L might be preferable to 2.5 or 3.0 mEq/L because it is associated with mildly positive tCa mass balance values, plasma water iCa levels in the reference range, and stable PTH levels during dialysis. Am J Kidney Dis. 59(1): 92-101. (C) 2011 by the National Kidney Foundation, Inc.