Hyperphosphatemia in Chinese peritoneal dialysis patients with and without residual kidney function: what are the implications?

Hyperphosphatemia is an important predictor for mortality in hemodialysis patients. This study evaluated significant factors associated with hyperphosphatemia in peritoneal dialysis (PD) patients.We estimated residual renal function (RRF), dialysis adequacy, and normalized protein equivalent nitrogen appearance (nPNA), together with simultaneous measurement of serum phosphorus levels in 252 prevalent Chinese continuous ambulatory peritoneal dialysis (CAPD) patients.Average serum phosphorus level was 5.2 +/- 1.5 mg/dL (1.68 +/- 0.48 mmol/L). Serum phosphorus levels were 5.6 mg/dL or greater (> or =1.81 mmol/L) in 44.0% of anuric patients (n = 116) versus 28.7% of patients with RRF (n = 136; P = 0.012). Patients with RRF maintained serum phosphorus levels at or less than the median value (< or =5.1 mg/dL [< or=1.65 mmol/L]), with a total creatinine clearance (CCr) of 72 +/- 25 L/wk/1.73 m2 and nPNA of 0.94 +/- 0.19 g/kg/d in contrast to a total CCr of 63 +/- 22 L/wk/1.73 m2 (P = 0.031) and nPNA of 1.03 +/- 0.22 g/kg/d (P = 0.011) in patients with serum phosphorus levels greater than the median value. Among anuric patients, total CCrs were 46 +/- 9 and 42 +/- 7 L/wk/1.73 m2 (P = 0.005) and nPNA values were 0.89 +/- 0.17 and 0.98 +/- 0.18 g/kg/d (P = 0.010) for patients with serum phosphorus levels at the median value or less and greater than the median value, respectively. Multiple regression analysis showed that residual glomerular filtration, despite an average of less than 2 mL/min/1.73 m2, was independently associated with phosphorus control in PD patients. nPNA, PD CCr or urea clearance, body mass index, and parathyroid hormone level were other important correlates of serum phosphorus levels in patients with and without RRF.Hyperphosphatemia is a frequent complication in Chinese CAPD patients. Our study not only shows the importance of RRF in maintaining serum phosphorus levels in PD patients, but also the limitations of PD alone to achieve adequate phosphorus control in anuric patients.