Peritoneal Phosphate Clearance: The Effect of Peritoneal Dialysis Modality and Peritoneal Transport Status

Hyper- and hypophosphatemia are recognized risk factors for all-cause mortality in peritoneal dialysis (PD) patients. Recent changes have now focused PD solute clearance targets on urea clearance, rather than on larger solutes, including phosphate. We therefore studied peritoneal phosphate clearance in a cohort of PD patients to determine which factors were clinically relevant.We reviewed results from 451 adult PD patients who were attending for their first assessment of peritoneal membrane function [31.2% treated by continuous ambulatory PD (CAPD); 24.2.%, by automated PD (APD); and 44.6% by APD with a daytime exchange]. Demographics, PD adequacy parameters, peritoneal phosphate clearance, and transport status were reviewed.Of the study patients, 119 (26.4%) were hyperphosphatemic, and 59 (30.1%) were hypophosphatemic; 22.2% were fast transporters. Total daily peritoneal phosphate losses were greater for the hyperphosphatemic than for the hypophosphatemic patients [15 mg/ dL (range: 10.5-18.6 mg/dL) vs. 25.7 mg/dL (range: 15.5-29.8 mg/dL), p < 0.01], although peritoneal phosphate clearance was less [2.7 mL/min/1.73 m² (range: 1.6-4.1 mL/min/1.73 m²) vs. 4.2 mL/ min/1.73 m² (range: 2.1-4.1 mL/min/1.73 m²), p < 0.001]. Peritoneal phosphate clearance was greater for faster compared with slower transporters [3.5 mL/ min/1.73 m² (range: 2.5-4.5 mL/min/1.73 m²) vs. 1.6 mL/min/1.73 m² (range: 1.1-2.2 mL/min/1.73 m²), p < 0.05] and for patients treated either with APD plus a daytime exchange or with CAPD compared with APD alone [3.44 mL/min/1.73 m² (range: 2.3-5.0 mL/ min/1.73 m²) vs. 2.9 mL/min/1.73 m² (range: 1.5- 4.4 mL/min/1.73 m²) vs. 1.6 mL/min/1.73 m² (range: 1.1-2.4 mL/min/1.73 m², p < 0.001)]. On multivariate analysis, increased peritoneal clearance was associated with faster peritoneal transport status, younger age, lower serum albumin, and lower serum phosphate.Peritoneal phosphate clearance depends not only PD modality, but also patient factors, including peritoneal transport status and variables associated with inflammation.