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Information About

Urea Reduction Ratio





DEFINITION

URR = rac{U_{pre}-U_{post}}{U_{pre}} imes 100\%

Where:
  • Upre is the pre-dialysis Urea level

  • Upost is the post-dialysis urea level



STANDARD DOSE

In the standard thrice hemodialysis schedule a URR of 65% is considered the minimum acceptable dose.


URR IN FREQUENT DIALYSIS

The URR decreases if dialysis is done more frequently, as the mass removed is spread over more dialysis sessions. A lower URR under these conditions does not necessarily mean that the dialysis is inadequate.


RELATION OF URR TO MASS TRANSFER

The Numerator of the URR definition is the removal of urea in the dialysis session, if the urea produced during the dialysis is ignored. In steady state, if the generation of urea is a constant, the URR is proportional to 1/Upre.


RELATION TO KT/V

Kt/V is another measure of dialysis. It is related to the URR by the following relationship:

rac{K \cdot t}{V} = -ln (1-URR)

Since the URR and Kt/V are related their predictive power is similar.


HISTORY

The URR was introduced by Lowrie and Lew in 1991.Shinaberger JH. Quantitation of dialysis: historical perspective. Semin Dial. 2001 Jul-Aug;14(4):238-45. PMID 11489196.


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