[The pitfalls of the clearance concept in hemodialysis]

The "clearance concept" is rigorously defined by the physicists and bioengineers. However its extension in clinical routine of dialysis therapy is not easy, but essential also to understand the rationale on which is based the currently widely used Kt/V index. The purpose of this paper is to describe the difficulties and pitfalls encountered in measuring the clearance of a substance either provided by a dialyzer or observed in a dialyzed patient. Ambiguities in the definition of clearance may account for sometimes moot estimations of the Kt/V index.