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Technical aspects of hemodiafiltration

James Tattersall, MD, MRCP
Peter J Blankestijn, MD
Section Editor
Paul M Palevsky, MD
Deputy Editor
Alice M Sheridan, MD


Hemodiafiltration (HDF) is a form of renal replacement therapy that utilizes convective rather than diffusive clearance. Compared with hemodialysis, HDF allows increased clearance of larger-molecular-weight toxins. Some, though not all, studies have suggested that HDF is associated with improved clinical outcomes.

However, HDF is more complex than standard hemodialysis and places increased demands on the user and manufacturer.

This topic reviews the technical aspects of HDF.


Conventional hemodialysis clears uremic toxins mostly by diffusion driven by the thermal energy of the uremic toxin molecule. Clearance of the toxin by diffusion is inversely proportional to the radius of the toxin molecule. As a result, conventional hemodialysis clears larger toxin molecules less effectively than smaller ones. Clearance of larger toxins is limited by their low rate of diffusion, even if they can easily pass through the pores in the dialyzer membrane.

In contrast, hemodiafiltration (HDF) increases the clearance of larger toxins by large-volume ultrafiltration. Ultrafiltration carries toxins through the membrane pores by fluid flow, also known as convection. As long as the toxin molecule can easily pass through the membrane pores, the rate of transfer is independent of the molecule size.


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Literature review current through: Nov 2016. | This topic last updated: Thu Nov 12 00:00:00 GMT+00:00 2015.
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