About \( FE_{Na} \) Calculator

The \( FE_{Na} \) Calculator is used to calculate the fractional excretion of sodium.

\( FE_{Na} \) Definition

The fractional excretion of sodium (abbreviated as \( FE_{Na} \) ) 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.

Formula

The \( FE_{Na} \) calculation formula is as follows:

\( FE_{Na} = (U_{Na} × P_{Cr}) / (U_{Cr} × P_{Na}) × 100% \)

Interpretation

\( FE_{Na} \) 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.