FEUrea Calculator

How does this FEUrea Calculator work?

This is a health tool allowing you to determine the fractional excretion of urea of use in certain nephrology fields. It is based on four simple available tests of the renal function and delivers a indicative percentage of renal failure and its likely cause. The FEUrea calculator uses the following formula:

FEUrea (percent) = (S_Cr x U_Urea) / (S_Urea x U_Cr) x 100

Where:

- S_Cr – serum creatinine – represents the waste product creatinine that is still in the body due to decreased kidney function. The normal values range between 0.6 to 1.3 mg/dL with small differences for each gender as women usually have lower levels of creatinine because they have a lower muscle mass.
- U_Cr – urine creatinine – is the removing product of creatinine through urine and its normal range is of 20- 320 mg/dL showing the efficiency of daily kidney excretion.
- S_Urea or BUN – serum urea or blood urea nitrogen – is the final stage of protein and amino acid degradation.  Normal range is between 6 – 21 mg/dL. Increased BUN levels indicate prerenal causes (increased protein catabolism, water depletion), renal causes (acute glomerulonephitis, chronic nephirtis, polycystic kidney disease).
- U_Urea – urine urea – represents the assessment of the protein breakdown and check whether the kidneys are excreting the right amount. Normal range varies from 12-20 grams/day.

Example calculation

Let’s take the case of a patient with the following test results: S_Cr = 14 mg/dL, U_Cr = 16 mg/dL, BUN = 11 mg/dL and U_Urea = 8 mg/dL. The result in this case is:

- FEUrea = 63.6 %;

- FEUrea interpretation: intrinsic renal pathology.

Medical implications of fractional excretion of urea

- This is a test indicated in acute kidney injuries as it distinguished between prerenal failure and instrinsic renal failure.
- It represents and alternative to the fractional excretion of sodium FENa for certain patients, because unlike the FENa determination, this is more specific and not altered by diuretic use.
- A percent below 35 indicate prerenal failure etiology while percents above 50 suggest an intrinsic renal disease.

Reference

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