Adequacy of Dialysis: Marker Molecules and Kinetic Modeling

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Abstract
The effective use of kinetic modeling to assess adequacy of dialysis, based upon marker molecules, is in its infancy. However, for the patient, perhaps the most identifiable benefit of modeling is that the technical parameters of the therapy are at least being measured and monitored. With regard to choice of marker molecules, the National Dialysis Cooperative Study (NCDS) group, in choosing urea as the reference molecule, has given a useful impetus to its wider use. Since urea is directly connected with dietary protein intake and its net generation is also directly correlated with that of other metabolites, its application as a marker molecule makes good sense. Analysis of the NCDS data has permitted identification of a very useful quantitative parameter of minimal dialysis therapy based on urea clearance and distribution volume and dialysis time. For thrice-weekly dialysis, normalized whole body urea clearance (Kt/V) should be greater than or equal to 1.0 and less than approximately 1.5. Although this alone does not guarantee adequate dialysis, it does alert the dialysis staff to the potential for both under- and over-dialysis. It would thus appear that currently the most reliable and useful means by which to apply modeling techniques to dialysis therapy is urea kinetics. In time, the application of more broad-based modeling techniques to dialysis therapy will provide more clearly identifiable clinical benefits, as well as the already realizable economic benefits.