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  FENa - Fractional Excretion of Sodium  

Serum Sodium (mmol/L)
Urine Sodium (mmol/L)
Serum Creatinine (mmol/L)
Urine Creatinine (mmol/L)
FENa (%)
 

Calculation(s) used


where
PCr = Plasma Creatinine (mmol/L), PNa = Plasma Sodium (mmol/L)
UCr = Urine Creatinine (mmol/L), UNa = Urine Sodium (mmol/L)
FENa = Fraction of sodium excretion

Notes

FENa is the percentage of the sodium filtered by the kidney which is excreted in the urine and is useful in the evaluation of acute renal failure and oliguria.

NB: FENa should not be used for patients taking diuretics as this will affect renal sodium reabsorption. Use FEUrea (Fractional excretion of Urea) instead

Interpretation

A FENa of less than 1% indicates decreased blood flow to the kidney (pre-renal), while a FENa greater than 1% (and usually greater than 3%) suggests kidney damage (renal/intrinsic).[1,2]

 
References
1. Steiner R (1984). "Interpreting the fractional excretion of sodium". Am J Med 77 (4): 699–702
2. Kumar, P. and Clark, M., eds. (2005). Clinical Medicine. 4th ed. Edinburgh : Elsevier Saunders.
3. MedlinePlus, Fractional excretion of Sodium [Retrieved 14/10/2010]

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