Convective therapies for removal of middle molecular weight uremic toxins in end-stage renal disease: a review of the evidence.

The increasing number of patients requiring renal replacement therapy poses a challenge to maintain quality of care in the setting of limited resources. The commonly used modalities include hemodialysis and peritoneal dialysis, and using a "urea-centric" model to increase the clearance of small molecular weight uremic toxins beyond current guidelines does not appear to confer additional clinical benefits in terms of morbidity and mortality. Convective therapies including hemofiltration and hemodiafiltration, which also have higher middle molecule clearances, might offer significant benefits compared to diffusive therapy. We review the available evidence on convective therapies and their effects on middle molecular weight uremic toxins, particularly beta2 microglobulin because of its known associated morbidity. It is the authors' opinion that more emphasis should be placed on true uremic toxins such as beta2 microglobulin rather than surrogate uremic toxins like urea. Larger studies are also needed to study the merits of convective therapies, with a focus on cardiovascular morbidity and mortality.