This residual renal function for hemodialysis calculator evaluates kidney residual function based on blood urine nitrogen, urinary volume and urea concentration. In the text below the form there are instructions on the available measurement units and the formulas used in this RRF calculator.

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:*

How does this residual renal function for hemodialysis calculator work?

This health tool determines the mean blood urea nitrogen value and the residual renal function based on urine volume, BUN after first dialysis of the week and prior to second dialysis of the week.

The residual renal function (RRF) calculator helps with the monitoring of RRF for preservation aims and in order to decrease mortality in associated renal disease:

■ Interdialytic urine volume – default measure in mL but fL and L also available;

■ Urine urea concentration – default measure is mg/dL but the determination can also be input in mg%, g/dL, g/L, mg/L, mcg/dL, mcg/mL or ng/mL;

■ Interdialytic period –  time in minutes, possibly input in hours or seconds as well;

■ BUN 1 – after first dialysis of week and BUN 2, prior to second dialysis of week, with values in mg/dL or mg%, g/dL, g/L, mg/L, mcg/dL, mcg/mL, ng/mL;

■ Mean BUN and residual renal function measurement unit – where users can select their preferred unit for the display of results.

The formulas employed are the following:

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

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

The urine urea nitrogen test measures the concentration of the waste product in urine (urea) and evaluates protein breakdown as function of kidney work and dietary protein intake.

The blood urea nitrogen test indicates kidney function and has normal ranges between 6 – 20 mg/dL. Increased values are due to high protein, decreased GFR, congestive heart failure, gastrointestinal hemorrhage or infection. Decreased values are consistent with severe kidney disease or syndrome of inappropriate antidiuretic hormone.

Residual renal function (RRF) guidelines

This is defined as urinary clearance of urea and creatinine and can have a significant impact on preventing mortality in patients with end-stage renal disease treated with peritoneal dialysis.

In patients undergoing hemodialysis, residual renal function usually has low values.

The residual renal urea clearance (KrU) is used in the dialysis prescription and the results in most studies show that it can be calculated the measurement of a single dialysis pre- and post-BUN and serum Cr in conjunction with urine collection volume.

Preservation of RRF is higher with peritoneal dialysis than with hemodialysis but discussions on whether the type of dialyzer membrane affects RRF are still ongoing.

Factors that are found to affect kidney residual function include:

■ Age – higher loss with age;

■ Gender – females increased risk of accentuated loss;

■ Race – non-white race higher loss;

■ High serum calcium – found to prevent loss of function.


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

2) Shemin D, Bostom AG, Laliberty P, Dworkin LD. (2001) Residual renal function and mortality risk in hemodialysis patients. Am J Kidney Dis Jul; 38(1):85-90.

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

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.

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

29 May, 2016