Calcium and Phosphorus Balance in Chinese Continuous Ambulatory Peritoneal Dialysis Patients

Abstract

Hyperphosphatemia is common in dialysis patients and is influenced significantly by dietary protein intake. In this study, we investigated phosphorous control and the metabolic balance of phosphorus and calcium in our peritoneal dialysis patients. Forty-one clinically stable continuous ambulatory peritoneal dialysis patients using peritoneal dialysis solution with a calcium concentration of 1.75 mmol/L participated in the study. Calcium carbonate was used as the phosphate binder. Dietary calcium, phosphorus, and protein intake were calculated for each patient from a 3-day dietary record; 24-hour urine, dialysate, and fasting blood were collected, and calcium, phosphorus, and protein levels in serum, urine, and dialysate were measured. Dietary protein, phosphorus, and calcium intake were 0.79 ± 0.27 g/kg/day, 595.9 ± 174.8 mg/day, and 441.9 ± 212.7 mg/day, respectively. Peritoneal dialysis removed 241.9 ± 87.2 mg/day phosphorus, whereas 45.4 ± 65.8 mg phosphorus was removed via urine. Hyperphosphatemia (> 1.8 mmol/L) occurred in 53.7% of patients despite the fact that 61% of hyperphosphatemic patients received calcium carbonate. A mean of 52.6 ± 83.5 mg/day calcium was absorbed from the dialysis solution. Eight patients (19.5%) presented with hypercalcemia. Serum phosphorus level correlated significantly with dietary protein intake ( r = 0.508, p < 0.01). However, the serum calcium level did not correlate with calcium intake from diet or dialysate. The incidence of hyperphosphatemia is still relatively high despite the low protein and low phosphorus intake in our peritoneal dialysis patients. A positive calcium balance was common in our patients using dialysis solution containing 1.75 mmol/L calcium, which needs to be further studied.