FENa Calculator

This is an online FENa calculator. You can use it to calculate the fractional excretion of sodium.

What is FENa?

The fractional excretion of sodium (abbreviated as FENa) is the percentage of the sodium filtered by the kidney which is excreted in the urine. It is measured in terms of plasma and urine sodium, rather than by the interpretation of urinary sodium concentration alone, as urinary sodium concentrations can vary with water reabsorption.

FENa formula

The equation used by our FENa calculator is:

FENa = (UNa × PCr) / (UCr × PNa) × 100%


  • PCr stands for plasma creatinine;
  • PNa stands for plasma sodium;
  • UCr stands for urine creatinine;
  • UNa stands for urine sodium.

Interpreting FENa

FENa Value Category Description
< 1% prerenal disease the physiologic response to a decrease in renal perfusion is an increase in sodium reabsorption to control hypovolemia.
> 2% or 3% acute tubular necrosis or other kidney damage either excess sodium is lost due to tubular damage, or the damaged glomeruli result in hypervolemia resulting in the normal response of sodium wasting.
intermediate either disorder In renal tract obstruction, values may be either higher or lower than 1%. The value is lower in early disease, but with renal damage from the obstruction, the value becomes higher.


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