Hemodialysis Residual Renal Function Calculator

Evaluates how well kidneys perform in patients under hemodialysis, based on blood urine nitrogen, urinary volume and urea concentration.

In the text below the form there is more information about the RRF calculation method.

The residual renal function calculator determines the RRF, which is a measure of how efficient the kidney function is, based on values from specialist determinations (blood urine nitrogen, urinary volume and urea concentration).

This calculator is addressed to patients who undergo hemodialysis and therefore subsequent BUN determinations are accounted for. The RRF helps clinicians monitor kidney disease and reduce associated mortality risks.

The formula used to determine residual renal function is:

RRF = Interdialytic urine volume x Urine urea concentration / Interdialytic period / Mean BUN


Mean BUN = (BUN 1 + BUN 2) / 2

Interdialytic urine volume
Urine urea concentration
Interdialytic period
BUN 1 (after 1st dialysis of week)
BUN 2 (prior to 2nd dialysis of week)
Mean BUN measurement unit
Residual renal function measurement unit
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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.


Variables and formula

The above calculator determines both the mean blood urea nitrogen and residual renal function, the first being also a precursor value for the calculation of the second.

This tool is to be used in patients with renal disease who undergo hemodialysis.

The variables involved in the calculation and the measurement units that can be selected are described in the table below:

RRF variable Default unit Other units
Interdialytic urine volume millilitres (mL) litres (L)
Urine urea concentration* mg/dL mg%, g/dL, g/L, mg/L, mcg/dL, mcg/mL or ng/mL
Interdialytic period minutes hours or seconds
BUN 1 and BUN 2** mg/dL mg%, g/dL, g/L, mg/L, mcg/dL, mcg/mL or ng/mL

* The urine urea nitrogen test determines the concentration of the waste product in urine (urea) and evaluates protein breakdown. These can offer information about the kidney function and reflect dietary protein intake.

**BUN 1 is the blood urea nitrogen determined after first dialysis of the week while BUN 2 is determined right before the second dialysis of the week.

The blood urea nitrogen test indicates kidney function and the values increase due to high protein and decreased GFR.

Low BUN indicates congestive heart failure, gastrointestinal hemorrhage or infection.

High BUN values are consistent with severe kidney disease or syndrome of inappropriate antidiuretic hormone.

The formulas employed are the following:

Residual Renal Function = Interdialytic urine volume x Urine urea concentration / Interdialytic period / Mean BUN


Mean BUN = (BUN 1 + BUN 2) / 2


About residual renal function

RRF is linked to the urinary clearance of urea and creatinine and is of capital importance in patients treated with peritoneal dialysis because, if kept under control, can prevent high rates of mortality from end-stage renal disease.

The residual renal urea clearance (KrU) is used in the dialysis prescription and as variable in several clinical studies. KrU can be defined as pre- and post- BUN and serum creatinine levels in conjunction with urine collection volume.

RRF tends to be higher in peritoneal dialysis than in hemodialysis, the first preserving better the renal residual function, but there is still controversy as to whether the type of dialyzer membrane really affects RRF.

RRF is affected by individual factors such as patient age, gender (women tend to have an increased risk of accentuated loss), race (non-white race has lower values). High serum calcium levels were found to prevent loss of function.



1. Daugirdas JT, Ing TS. (1994) Handbook of Dialysis. Second Edition pp 92-107.

2. Wang AY, Lai KN. The importance of residual renal function in dialysis patients. Kidney Int May. 2006; 69(10):1726-32.

3. Thomas J, Teitelbaum I. Preservation of residual renal function in dialysis patients. Adv Perit Dial. 2011; 27:112-7.

4. Moist LM, Port FK, Orzol SM, Young EW, Ostbye T, Wolfe RA, Hulbert-Shearon T, Jones CA, Bloembergen WE. (2000) Predictors of loss of residual renal function among new dialysis patients. J Am Soc Nephrol Mar; 11(3):556-64.

Specialty: Nephrology

System: Urinary

Objective: Determination

Type: Calculator

No. Of Variables: 5

Abbreviation: RRF

Article By: Denise Nedea

Published On: June 22, 2017 · 07:25 AM

Last Checked: June 22, 2017

Next Review: June 22, 2023