Urea Reduction Ratio (URR) Calculator

Quantifies hemodialysis efficiency based on pre and post urea levels.

Information about the formula used and the importance of the urea reduction rate can be found in the text below the form.

The urea reduction ratio calculator checks the efficiency of hemodialysis based on pre and post urea levels.

The URR is also known as the urea reduction percentage and facilitates a quick monitoring of dialysis parameters.

The two variables used: pre and post urea can be input in a variety of measurement units: mg/dL, g/L, g/dL, mg% and mg/L.

The URR formula is:

URR = (Upre - Upost)/Upre x 100 = (1 - Upre/Upost) x 100

Pre-dialysis urea level (Upre)
Post dialysis urea level (Upost)
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Steps on how to print your input & results:

1. Fill in the calculator/tool with your values and/or your answer choices and press Calculate.

2. Then you can click on the Print button to open a PDF in a separate window with the inputs and results. You can further save the PDF or print it.

Please note that once you have closed the PDF you need to click on the Calculate button before you try opening it again, otherwise the input and/or results may not appear in the pdf.


URR formula

The urea reduction ratio or the urea reduction percentage (PRU) can be used to monitor dialysis efficiency based on pre- and post-dialysis urea nitrogen levels which are measured on a routine basis, each month or every 12-14 dialysis sessions.

The pre- and post- urea levels can be input in any of the following five measurement units: mg/dL, g/L, g/dL, mg% or mg/L.

This is the formula used by the URR calculator:

URR = (Upre - Upost)/Upre x 100 = (1 - Upre/Upost) x 100

By providing insight on the amount of dialysis when the clearance of urea exceeds the urea generation rate, the URR shows whether the set dialysis rate is able to remove waste products from the body. This efficiency is expressed as a percentage.


URR and Kt/V

URR values lower than 60% indicate high levels of urea build up and increased adverse outcome. In some cases deficitary nutrition can worsen the status of the patient.

URR is linked to Kt/V which is one of the main methods of dialysis measurement.

Kidney Disease Outcomes Quality Initiative (K/DOQI) national guidelines suggest that dialysis is efficient when Kt/V is at least 1.2.

The relationship between the two is exemplified by the following equation:

(K x t)/V= -ln(1 - URR)


■ K – dialyzer clearance – blood passage rate in mL/min;

■ t – duration of dialysis;

■ V – volume of bodily water.



1. Owen WF, Lew NL, Liu Y, Lowrie EG, Lazarus JM. The Urea Reduction Ratio and Serum Albumin Concentration as Predictors of Mortality in Patients Undergoing Hemodialysis. N Engl J Med. 1993; 329:1001-1006.

2. Kessler E, Ritchey NP, Castro F, Caccamo LP, Carter KJ, Erickson BA. Urea reduction ratio and urea kinetic modeling: a mathematical analysis of changing dialysis parameters. Am J Nephrol. 1998; 18(6):471-7.

3. Powers KM, Wilkowski MJ, Helmandollar AW, Koenig KG, Bolton WK. (2000) Improved urea reduction ratio and Kt/V in large hemodialysis patients using two dialyzers in parallel. Am J Kidney Dis. 2000; 35(2):266-74.

Specialty: Nephrology

System: Urinary

Objective: Determination

Type: Calculator

No. Of Variables: 2

Abbreviation: URR

Article By: Denise Nedea

Published On: April 6, 2017

Last Checked: April 6, 2017

Next Review: April 6, 2023