Peritoneal Dialysis International, Vol. 29, pp. 465–471 Printed in Canada. All rights reserved. 0896-8608/09 $3.00 + .00 Copyright © 2009 International Society for Peritoneal Dialysis 465 DIALYTIC PHOSPHATE REMOVAL: A MODIFIABLE MEASURE OF DIALYSIS EFFICACY IN AUTOMATED PERITONEAL DIALYSIS Claus P. Schmitt, 1a Dagmara Borzych, 1,2a Barbara Nau, 1 Elke Wühl, 1 Aleksandra Zurowska, 2 and Franz Schaefer 1 Division of Pediatric Nephrology, 1 Center for Pediatric and Adolescent Medicine, University of Heidelberg, Germany; Department of Pediatric Nephrology, 2 Medical University of Gdansk, Poland a These authors contributed equally to this study. Correspondence to: F. Schaefer, Division of Pediatric Nephrology, University Children’s Hospital, Im Neuenheimer Feld 151, 69120 Heidelberg, Germany. franz.schaefer@med.uni-heidelberg.de Received 5 May 2008; accepted 12 September 2008. ♦ Background: Although hyperphosphatemia is one of the few established risk factors for cardiovascular mortality in patients on dialysis, the relationship between peritoneal dialysis (PD) prescription and dialytic phosphate removal is largely unexplored. ♦ Methods and Patients: We analyzed 24-hour clearances (n = 60) together with peritoneal equilibration tests (PETs) (n = 52) performed in children and adolescents (n = 35) on automated PD. ♦ Results: Dialytic phosphate clearance was more closely cor- related with 2-hour and 4-hour dialysate-to-plasma ratio (D/P) of phosphate in the PETs (r = 0.44 and r = 0.52, both p < 0.0001) than with 2-hour and 4-hour D/P creatinine (r = 0.26 and r = 0.27, both p < 0.05). Dialytic 24-hour phosphate clearance was independently predicted by total fluid turn- over (partial R 2 = 0.48, p < 0.001), the number of cycles (r = 0.52, p < 0.001), 2-hour D/P phosphate (partial R 2 = 0.07, p = 0.001), dwell time (partial R 2 = 0.05, p = 0.01), and achieved ultrafiltration (partial R 2 = 0.05, p = 0.005). 4-hour D/P phosphate and 24-hour phosphate clearance were sig- nificantly lower in hyperphosphatemic children (3.38 ± 1.17 vs 4.56 ± 1.99 L/1.73 m 2 /day, p < 0.05), whereas creatinine equilibration and clearance rates were not distinctive. ♦ Conclusion: Dialytic phosphate removal is an important modifiable determinant of phosphate control in automated PD. It strongly depends on total dialysate turnover and the prescribed number of cycles and is more adequately predicted by phosphate than by creatinine equilibration characteris- tics. Due to the deleterious effects of hyperphosphatemia, dialytic phosphate removal should be monitored routinely. Perit Dial Int 2009; 29:465–471 www.PDIConnect.com KEY WORDS: Phosphate clearance; peritoneal trans- port; adequacy; children. T he definition of peritoneal dialysis (PD) adequacy has long been a matter of controversy. Extending the urea kinetic modeling approach of hemodialysis, small-mol- ecule clearances were originally considered useful prognostically relevant indices of PD dose. Observational studies such as the CANUSA trial suggested a linear re- lationship between urea and creatinine clearance and patient mortality and morbidity (1), and resulted in the formulation of adequacy guidelines defining dialysis adequacy by certain minimum urea and creatinine clear- ances (2). However, subsequent interventional trials demonstrated that modification of dialytic small- molecule removal does not affect patient survival or mor- bidity (3,4). Hence, the search for a prognostically useful marker of dialysis adequacy continues. Hyperphosphatemia has been identified as a signifi- cant risk marker of cardiovascular and all-cause mortal- ity in adult dialysis patients (5–10). Mechanistically, the link between hyperphosphatemia and mortality has been attributed to disseminated vascular calcifications in pa- tients on chronic dialysis. Calcifying large-vessel arteriopathy develops even in young patients with child- hood-onset end-stage renal disease (ESRD) and is asso- ciated with the prevailing calcium–phosphorus ion product (11,12). These findings raise the issue of whether dialytic phosphate removal might provide a more rel- evant direct measure of dialysis efficacy and adequacy than urea and creatinine clearance. In contrast to the large body of research available on the peritoneal trans- port kinetics and daily dialytic clearance of urea and creatinine, surprisingly little is known about the capac- ity to remove phosphate via the peritoneal membrane, although its importance is apparent and has been em- phasized (13,14). Previous studies suggest that phos- phate removal can be improved by modification of the dwell time (15,16); however, a detailed analysis of the