Satisfactory control of secondary hyperparathyroidism with low-calcium dialysate in patients not receiving vitamin D

The use of a dialysate calcium concentration of 2.5 mEq/1 for patients not receiving vitamin D is controversial. Therefore, it has been suggested that oral calcium supplements might be sufficient to avoid a negative calcium balance which could result in a worsening of secondary hyperparathyroidism. In order to clarify these aspects, we reduced the dialysis fluid calcium level in 26 patients on chronic hemodialysis with a dialysate calcium concentration of 3.25 mEq/l, all of them receiving low doses of calcium carbonate and aluminum hydroxide. No patient received supplements with vitamin D during the previous 2 years. These patients have been dialyzed using a dialysate calcium concentration of 2.5 mEq/l for 1 year. Gradually we increased the dose of calcium carbonate and decreased the dose of aluminum hydroxide to maintain the predialysis serum calcium and phosphate concentrations between 8-10 and 4-6 mg/dl, respectively. After 1 year of hemodialysis with a low-calcium dialysate (2.5 mEq/l), the oral dose of calcium carbonate was increased from 3.5 +/- 2.6 to 9.2 +/- 5.6 g/day (p < 0.001). In 22 patients (85%) the aluminum hydroxide was stopped, and in the remaining 4 cases the dose was lowered. The reduction in the dialysate calcium concentration did not increase the incidence of hypercalcemia or hyperphosphatemia. In the whole group, we did not observe a significant variation in the levels of intact parathyroid hormone (iPTH; 324 +/- 123 vs. 311 +/- 256 pg/ ml) or alkaline phosphatase (230 +/- 115 vs. 224 +/- 127 U/l), although there was a reduction in the serum aluminum concentration (33 +/- 31 vs. 21.8 +/- 20.2 micrograms/l; p < 0.001). We analyzed the evolution of iPTH in each case. In 15 patients (58%) the iPTH concentration decreased, in 6 cases (23%) it remained stable, and in only 5 subjects (19%) there was an increase (2 of them did not take the oral calcium dosage recommended). In conclusion, a low dialysate calcium concentration (2.5 mEq/l) is safe for most patients not receiving vitamin D. But adherence of patients to high doses of oral calcium supplements is absolutely necessary.