Removal of the protein-bound solute p-cresol by convective transport: a randomized crossover study

Middle molecules (MMs) and protein-bound solutes are poorly removed by conventional hemodialysis (HD). Hemodiafiltration (HDF) combines convection and diffusion in a single therapy and has been shown to be superior for the elimination of several small and larger retention molecules. Information on the elimination of protein-bound solutes during convective strategies is scarce. The primary aim of this randomized crossover study is to evaluate the influence of internal filtration, postdilution HDF, and predilution HDF on removal of the protein-bound solute p-cresol.

Fourteen stable patients on regular thrice-weekly medium-flux HD therapy were assigned to 5 treatment periods of 2 weeks each for: HD with HF80(S); HD with FX80; postdilution HDF, 20 L, with FX80; predilution HDF, 20 L, with FX80; and predilution HDF, 60 L, with FX80 (all dialyzers from Fresenius Medical Care, Bad Homburg, Germany).

As for the water-soluble solutes, elimination of p-cresol was better during HDF and increased with greater filtration volumes. Removal of beta2-microglobulin (beta2m) also was enhanced during HDF. However, the positive effect of convection was offset when high predilution substitution volumes were applied, probably as a result of dilution. Within each dialytic approach, removal of the MM beta2m and the protein-bound solute p-cresol was significantly less than that of the water-soluble molecules urea nitrogen and creatinine.

Our data indicate that convection can provide superior protein-bound solute removal compared with high-flux HD. Our findings also suggest that better elimination of the unbound fraction is the most plausible underlying mechanism.