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Why do patients on peritoneal dialysis have low blood levels of protein-bound solutes?

Nature Reviews Nephrology volume 5, pages 130–131 (2009)Cite this article

Studies that have compared the efficacy of peritoneal dialysis with that of hemodialysis have rarely evaluated the removal of protein-bound molecules, in spite of the pathophysiological importance of such molecules.1,2 Peritoneal dialysis, a strategy characterized by slow continuous removal of solutes, peritoneal albumin loss and improved preservation of residual renal function, should provide better removal of protein-bound solutes than does hemodialysis. Nevertheless, studies have indicated that clearance (i.e. the amount of blood purified per unit of time) and/or removal (i.e. the absolute quantity of solute eliminated over time) of the protein-bound solutes p-cresol, p-cresylsulfate and indoxyl sulfate is more efficient in patients on hemodialysis than in those on peritoneal dialysis.3,4 Paradoxically, however, the plasma concentration of these protein-bound solutes is lower in patients on peritoneal dialysis than in those on hemodialysis. Although this result was not emphasized in the original study reports, this finding is in our opinion more crucial than the difference in clearance, because lower plasma concentrations of protein-bound solutes have been directly linked to better outcomes.5 Knowledge of the factors that contribute to the apparent paradox of lower clearance with lower plasma concentration of protein-bound solutes in patients on peritoneal dialysis might help to explain the short-term survival advantage—or at least the absence of a survival disadvantage—conferred by peritoneal dialysis compared with hemodialysis.6,7

The first publication on this topic was a cross-sectional observational study by Evenepoel et al.,3 which compared ad hoc removal rates, clearances and serum concentrations of several uremic solutes, including p-cresol, in high-flux hemodialysis and peritoneal dialysis. Most of the patients in the peritoneal dialysis group were receiving automated peritoneal dialysis (APD). In patients with uremia, p-cresol is mainly present in the form of conjugates, such as p-cresylsulfate;8 p-cresol is a hydrolytic artifact generated by acidification of the blood sample during deproteinization. The removal of p-cresol can, however, be assumed to reflect that of the conjugates that are actually present in the blood.

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Acknowledgements

N Meert is the recipient of a doctoral grant from the Special Research Fund (Bijzonder Onderzoeksfonds), Flanders. S Eloot is employed by the Belgian Fund for Scientific Research, Flanders (FWO–Vlaanderen).

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Authors and Affiliations

  1. R Vanholder is Head of the Nephrology Section at the University Hospital of Ghent, N Meert is a Doctoral Student in the Laboratory of the Nephrology Section at the University Hospital of Ghent, W Van Biesen and A Dhondt are Chief Clinicians in the Nephrology Section at the University Hospital of Ghent, and S Eloot is a Postdoctoral Fellow at the Institute of Biomedical Technology, Ghent University, Ghent, Belgium.,

    Raymond Vanholder, Natalie Meert, Wim Van Biesen, Annemieke Dhondt & Sunny Eloot

  2. T Meyer is Section Chief at VA Palo Alto Health Care System, Palo Alto, CA,

    Timothy Meyer

  3. T Hostetter is Director of the Nephrology Division at the Albert Einstein College of Medicine, New York, NY, USA.,

    Thomas Hostetter

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  1. Raymond Vanholder
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  2. Natalie Meert
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Correspondence to Raymond Vanholder.

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Vanholder, R., Meert, N., Van Biesen, W. et al. Why do patients on peritoneal dialysis have low blood levels of protein-bound solutes?. Nat Rev Nephrol 5, 130–131 (2009). https://doi.org/10.1038/ncpneph1023

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