FEUrea Calculator

Determines the fractional excretion of urea based on serum and urea creatinine, BUN and urine urea.

In the text below the form you can read more about the variables and the formula used, along with information on the original study.

The FEUrea calculator uses the serum and urine creatinine, the blood urea nitrogen (serum urea) and urine urea, to compute the fractional excretion of urea.

This tool delivers an indicative percentage of renal failure and whether the etiology is prerenal or intrinsic renal disease.

The formula used is:

FEUrea (percent) = (SCr x UUrea) / (SUrea x UCr) x 100


■ FEUrea ≤35% indicates prerenal failure;

■ FEUrea >50% indicates intrinsic renal disease.

Serum Creatinine [SCr]
Urine Creatinine [UCr]
BUN/Serum Urea [SUrea]
Urine Urea [UUrea]
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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.


FEUrea formula

The FEUrea calculator determines the cause of renal failure based on the excretion of urea, a measure of renal function.

The four variables that determine FEUrea are:

Symbol Variable Definition Normal Other info
SCr Serum creatinine The waste product creatinine that is still in the body due to decreased kidney function 0.6 to 1.3 mg/dL Women have slightly lower values because of less muscular mass.
UCr Urine creatinine The removing product of creatinine through urine 20 to 320 mg/dL Indicates the efficiency of daily kidney excretion.
SUrea or BUN Serum urea or blood urea nitrogen The final stage of protein and amino acid degradation 6 to 21 mg/dL Increased BUN levels indicate prerenal causes (increased protein catabolism) or renal causes (acute glomerulonephritis, chronic nephritis).
UUrea Urine urea The assessment of protein breakdown 12 to 20 g/day Checks whether kidneys are excreting the right amount of protein.

The FEUrea formula is:

FEUrea (percent) = (SCr x UUrea) / (SUrea x UCr) x 100

The result in percent is interpreted as follows:

■ FEUrea ≤35% indicates prerenal failure;

■ FEUrea >50% indicates intrinsic renal disease.

The FENa determination is more common than FEUrea but the former can provide an alternative to the fractional excretion of sodium for patients under diuretic therapy because it is more specific and is not altered by diuretic use.

The correlation between the results from the two methods is:

Method Pre-renal cause Intrinsic renal cause Post-renal cause
FEUrea ≤35% >50% n/a
FENa <1% >1% >4%

About the study

During a study from 2002, Carvounis et al. were set to check whether FEUrea could be useful in the evaluation of acute renal failure.

To do so, the new method was compared to FENa in 102 episodes of ARF due to either prerenal azotemia or acute tubular necrosis.

Since FENa can be influenced in patients with prerenal disorders who receive diuretics (because of the decrease in sodium which decreases FENa), FEUrea was found to be a more sensitive and specific index than FENa in differentiating between acute renal failure due to prerenal azotemia and that due to acute tubular necrosis, especially when the patient is under diuretic therapy.


Original source

Carvounis CP, Nisar S, Guro-Razuman S. Significance of the fractional excretion of urea in the differential diagnosis of acute renal failure. Kidney Int. 2002; 62(6):2223-9.


Darmon et al. Diagnostic performance of fractional excretion of urea in the evaluation of critically ill patients with acute kidney injury: a multicenter cohort study. Crit Care. 2011; 15(4): R178.

Specialty: Urology

System: Urinary

Objective: Determination

Type: Calculator

No. Of Variables: 4

Year Of Study: 2002

Article By: Denise Nedea

Published On: May 30, 2017

Last Checked: May 30, 2017

Next Review: May 30, 2023