Changes in intact parathyroid hormone levels during hemodialysis following exposure to either differing dialyzate calcium concentrations or calcium-free dialysis with varying calcium infusion rates.

To determine the optimal infusion rate for calcium, when using a dialyzate which was calcium free, six patients were treated sequentially, in random order, with six different dialyzates. Three were calcium free and they were infused with replacement calcium at either 10, 15 or 20 ml/hour using 10% CaCl2. The other three used standard bicarbonate dialyzate with either 1.25, 1.5 or 1.75 mmol/l calcium. Ionized calcium and intact parathyroid hormone (Nichols IRMA PTH) were measured at the start and end of each dialysis. Ionized calcium rose slightly with 15 ml/hour calcium infusion and PTH fell 137 +/- 111 pg/ml. These changes were similar to those of 1.5 mmol/l calcium in standard bicarbonate. More PTH suppression and higher end dialysis calcium resulted from 20 ml/hour infusion or 1.75 mmol/l dialyzate calcium. It was concluded that 15 ml/hour is a suitable calcium infusion rate under normal conditions when using calcium-free dialyzate.