Effects of high dialysate calcium concentration on bone remodelling, serum biochemistry, and parathyroid hormone in patients with renal osteodystrophy.

The influence of a dialysate calcium concentration of 8.0 mg/100 ml (treatment period 2) vs. 7.0 mg/100 ml (treatment period 1) on plasma calcium, phosphorus, serum immunoreactive parathyroid hormone (iPTH), bone histology, intestinal calcium absorption, and calcium transfer across the dialysis membrane was investigated in six patients with renal osteodystrophy undergoing intermittent hemodialysis. During the periods 1 and 2, the plasma calcium changes before and after dialysis were not significantly different. A significant increase in mean postdialysis plasma calcium level was observed during both periods when compared to mean predialysis level. A significant, inverse relation was found between predialysis plasma calcium and the increase in plasma calcium during hemodialysis runs. Calcium transfer across the dialysis membrane and fractional intestinal absorption of calcium in the postdialysis state were determined in four out of the six patients. During period 2, calcium transfer was higher in all four patients but intestinal calcium absorption was moderately higher only in one and strikingly lower in the remaining three patients when compared to period 1. Although brought up to 8.0 mg/100 ml, this higher dialysate calcium significantly decreased the level of serum iPTH only in one out of the six patients; in this patient, osteoclast count, active resorption surface, and periosteocytic osteolysis decreased. In a second patient, although the level of serum iPTH seemed to decrease markedly osteoclastic and osteocytic resorption did not change. In the remaining four patients, the level of serum iPTH was unchanged and bone resorption parameters were found unchanged or aggravated. It is concluded that providing additional calcium (using a dialysate calcium concentration of 8.0 mg/100 ml), the goal of which was to decrease secondary hyperparathyroidism, proved to be successful only in one patient and failed to do so in the five others. Secondary hyperparathyroidism was even found aggravated in three of them. Thus, the use of a dialysate calcium concentration of 8.0 mg/100 ml did not result in any advantage over that of 7.0 mg/100 ml in five out of six patients studied.