Paired-filtration dialysis (PFD) is the only hemodiafiltration (HDF) technique in which ultrafiltrate (Uf) is obtained continuously with a similar composition to plasma. It has been proved that Uf is regenerated when it passes through an uncoated adsorbent charcoal cartridge: this one removes medium-to-large solutes and small toxines (except for urea and phosphates), but not the elecrolytes and bicarbonate
To improve the clearance of HDF , a modified technique was proposed that is able to make convective and diffusive solute mass transfer simultaneously but in two separate and consecutive chambers: a small hemofilter and a dialyzer (two chambers technique or paired filtration dialyzer [PFD]