Renal versus continuous versus intermittent therapies for removal of uremic toxins.

Uremic toxin removal by renal replacement therapies (RRTs) differs from the elimination of waste products by the native kidney in several ways. Specifically, uremic toxin removal by a RRT is achieved by a one-step membrane-based process, without the subsequent modifications that occur in the native kidney after a solute is filtered across the glomerular membrane. Another major difference relates to the continuous nature of native kidney function, which provides constant solute clearances and mass removal rates for a patient in steady state. This constancy of solute clearance, mass removal rate, and serum concentration does not exist for RRTs used in patients with end-stage renal disease (ESRD). The purpose of this review is first to compare solute removal by the native kidney with that by the various RRTs used for uremic patients. Subsequently, the therapy specificity of the relationship between solute clearance and mass removal rate is discussed, and the effective solute removal capabilities of different therapies compared.