A low calcium dialysate reduces hypercalcemia from calcium-containing phosphate binders and makes phosphate control possible without the use of aluminum salts. We asked whether this might, however, lead to hyperparathyroidism. We prospectively studied serum concentrations of parathyroid hormone levels (by an immunoreactive intact molecule assay) in 173 patients on continuous ambulatory peritoneal dialysis (CAPD) who were started on a low calcium dialysate (Ca2+ 1.25 or 1.00 mmol/L) because of hypercalcemia. Median follow-up was 13.2 months (range 1-28). Initial serum parathyroid hormone was [median(range)]: 70(5-1043) ng/L pre low calcium dialysate, and this rose to 130(5-914) ng/L at 0-6 months; 130(5-1030) ng/L at 6-12 months; 170(170-1400) ng/L at 12-18 months; and 130(5-1200) ng/L at 18-24 months (p = 0.0006). Twenty-two patients required a parathyroidectomy because of a sustained rise in parathyroid hormone that was not responsive to alfacalcidol and hypercalcemia. Initial serum parathyroid hormone was significantly higher in these patients at 359 (5-1073) ng/L as compared to a level of 69.5 (6-1147) ng/L in patients who did not have a parathyroidectomy (p = 0.0009). There was a significant sustained fall in mean serum corrected calcium from 2.77 (2.37-3.51) mmol/L to 2.53 (1.39-3.20) mmol/L at three months (p = 0.0006), a nonsignificant rise in mean serum alkaline phosphate from 179 (47-1858) mmol/L to 191 (55-1821) mmol/L (p = 0.15), and a fall in mean serum phosphate levels from 1.87 (0.59-3.18) mmol/L to 1.68 (0.45-3.6) mmol/L (p = 0.76). Our data suggest that the benefits of a low calcium dialysate in CAPD patients are balanced by an increased risk of hyperparathyroidism, and that this risk is higher in patients with an initially high serum parathyroid hormone level.

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