Phosphate Removal by Peritoneal Dialysis: The Effect of Transporter Status and Peritoneal Dialysis Prescription

Abstract

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Background: Interventional trials failed to demonstrate that increasing urea clearance improved peritoneal dialysis (PD) patient survival. Hyperphosphatemia is a well-recognized predictor of cardiovascular and all-cause mortality in PD patients. Simplification of PD small solute clearance targets focuses away from larger solutes, including phosphate. In the US and UK, increasing use of automated peritoneal dialysis (APD) cyclers with shorter dwell times could also potentially reduce peritoneal phosphate removal compared to continuous ambulatory peritoneal dialysis (CAPD). ♦

Methods: Total phosphate and peritoneal phosphate clearances were measured in a prospective observational cohort of 380 adult PD patients attending a tertiary university hospital between 1996 and 2013 for routine assessment of PD adequacy. ♦

Results: Eighty-seven patients (22.9%) were hyperphosphatemic. Taking the mean 4-hour dialysate to plasma (D/P) ratio for phosphate, 193 (50.8%) were fast and fast-average transporters and 187 (49.2%) were slow and slow-average transporters (compared to 276 [72.6%] and 104 [27.4%], respectively, for peritoneal creatinine transporter status). Faster peritoneal phosphate transporter status was associated with over-hydration (odds ratio [OR] = 2.45 [1.43 - 4.20], p = 0.001). Whereas the 4-hour D/P creatinine and peritoneal weekly creatinine clearance did not differ between those who were hyperphosphatemic or not, the hyperphosphatemic patients had lower 4-hour D/P phosphate and lower peritoneal weekly phosphate clearance (p = 0.019, and p = 0.06 respectively). We found greater peritoneal phosphate clearance for patients choosing CAPD compared to APD, irrespective of the peritoneal phosphate transporter status. ♦

Conclusion: Peritoneal creatinine transporter status and creatinine clearance cannot be used as surrogate markers of peritoneal phosphate transport and clearance. Hyperphosphatemia was more common in PD patients with slower peritoneal transporter status and lower peritoneal phosphate clearance. Greater peritoneal phosphate clearance was achieved with CAPD prescriptions. Slower peritoneal transporters should be advised to choose CAPD to improve serum phosphate control.

Keywords: APD; CAPD; Peritoneal dialysis; phosphate; residual renal function; transport.

Figure 1 —

Mean 4-hour D/P Phosphate (Pi) and D/P Creatinine (Cr) according to 4 categories of peritoneal phosphate and creatinine transport status. D/P Cr = dialysate to plasma ratio for creatinine; D/P Pi = dialysate to plasma ratio for phosphate.

Figure 2 —

Bland Altman plot peritoneal creatinine clearance and peritoneal phosphate clearance. PD Cr Cl = peritoneal dialysis creatinine clearance; PD Ph Cl = peritoneal dialysis phosphate clearance; D/P Cr = dialysate to plasma ratio for creatinine.