The urea reduction ratio (URR), is a dimensionless number used to quantify hemodialysis treatment adequacy.

Definition

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$URR\; =\; \backslash frac\{U\_\{pre\}-U\_\{post\}\}\{U\_\{pre\}\}\; \backslash times\; 100\backslash \%$

Where:

• U_pre is the pre-dialysis urea level
• U_post is the post-dialysis urea level

Standard dose

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

URR in frequent dialysis

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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

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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/U_pre.

Relation to Kt/V

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

$\backslash frac\{K\; \backslash cdot\; t\}\{V\}\; =\; -ln\; (1-URR)$

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

History

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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.

References

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See also

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• Clearance
• Hemodialysis

External links

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• Hemodialysis Dose and Adequacy - a description of URR and Kt/V from the Kidney and Urologic Diseases Clearinghouse.

Calculators

• Kt/V calculator - medindia.com
• TAC calculator - medindia.com
• Nephrology Calculator - does various renal calculations.

Nephrology