LOW-CALCIUM DIALYSIS FLUID AND ORAL CALCIUM-CARBONATE IN CAPD - A METHOD OF CONTROLLING HYPERPHOSPHATEMIA WHILE MINIMIZING ALUMINUM EXPOSURE AND HYPERCALCEMIA

Oral calcium carbonate is an effective phosphate binder in dialysis patients. Its use minimizes aluminium intake, and by maintaining a high-normal serum ionized calcium, suppresses serum parathyroid hormone levels. However, the dose required to control hyperphosphataemia may cause hypercalcaemia. We performed prospective studies in 50 previously undialysed patients starting CAPD (28 study group, 22 control group). Calcium carbonate was the only phosphate binder used in the study group which utilized a low calcium PD fluid (calcium 1.25 mmol/1), whilst the control group used standard PD solution (calcium 1.75 mmol/l) with calcium carbonate plus aluminium hydroxide phosphate binders as clinically indicated. The study group was able to take larger doses of oral calcium carbonate with no increase in episodes of hypercalcaemia compared to the control group. There were no instances of hypocalcaemia in any patient using the low-calcium dialysis fluid. Phosphate control was better in the study group, despite the additional use of aluminium-containing phosphate binders by some patients in the control group. Serum aluminium levels in the study group were maintained at < 11.5 mumol/l, but increased significantly in the control group from 3 months onward. Mean serum parathyroid hormone in the study group declined significantly from baseline values over the first 6 months, and remained at the lower level. Bone histology showed a tendency towards improvement over the 12 months, in terms of osteoclast numbers and activity. We conclude that using dialysis fluid with a reduced calcium concentration in compliant. well-monitored patients is safe. It allows administration of large doses of calcium carbonate to obtain good control of serum phosphate and maintain serum ionized calcium near the upper end of the normal range. Parathyroid hormone is suppressed in the majority of patients and bone histology improves. By utilizing this more physiological dialysis fluid, aluminium-containing phosphate binders may be completely avoided in most CAPD patients.