Low prevalence of hyperphosphatemia independent of residual renal function in peritoneal dialysis patients.

OBJECTIVE

Our objective was to evaluate serum phosphorus control in patients undergoing continuous ambulatory peritoneal dialysis, with and without residual renal function, by investigating the metabolic balance of phosphorus.

METHODS

We assessed serum phosphorus levels in 205 patients undergoing continuous ambulatory peritoneal dialysis (CAPD). The clinical factors related to serum phosphorus were also examined, including dietary phosphate intake, dietary protein intake (DPI), phosphate removal through urine and dialysate, doses of phosphorus binder and vitamin D, and serum intact parathyroid hormone (PTH) levels. Nutritional indexes, including serum albumin (Alb), lean body mass (LBM), hand-grip strength (HGS), and subjective global assessment (SGA), were also assessed. Dialysis adequacy and residual renal function (RRF) were calculated by a standard technique. Patients with RRF <2 mL/min were viewed as having no significant RRF. Hyperphosphatemia was diagnosed in patients with serum phosphorus levels >1.78 mmol/L.

RESULTS

The mean serum phosphorus level of all patients was 1.6 +/- 0.5 mmol/L (mean +/- SD). Only 58 of 205 patients (28%) had hyperphosphatemia. The average DPI was 0.8 +/- 0.3 g/kg/d, whereas the average dietary phosphorus intake was 691 +/- 201 mg/d. There were no differences in mean serum phosphorus levels or incidents of hyperphosphatemia between patients with and without RRF (1.6 +/- 0.4 mmol/L vs. 1.7 +/- 0.5 mmol/L, P = .256; 22% vs. 31%, P = .336). Although total phosphorus removal through urine and dialysate was lower in the 115 patients without RRF than in the 90 patients with RRF (270 +/- 106 mg vs. 333 +/- 129 mg, P = .000), they simultaneously had a lower dietary phosphorus intake (656 +/- 191 mg vs. 713 +/- 215 mg, P = .046). In addition, patients without RRF had significantly lower DPI, Alb, LBM, and right HGS levels than patients with RRF (P < .01-.05). In those without RRF, the 79 patients without hyperphosphatemia had significantly lower DPI, LBM, and HGS levels, and a higher prevalence of malnutrition diagnosed by SGA, than the 36 patients with hyperphosphatemia (P < .001-.05). However, in patients with RRF, there was no difference in nutritional index between patients with and without hyperphosphatemia (P > .05).

CONCLUSION

A relatively lower prevalence of hyperphosphatemia existed in CAPD patients both with and without RRF, which may be associated with incremental dialysis, the correct administration of phosphorus binder, and a lower protein and phosphorus intake. However, patients without RRF, especially those without hyperphosphatemia, ran the risk of malnutrition, despite a well-controlled phosphorus intake.