Fractional Excretion of Sodium (FENa)

Differentiate prerenal from intrinsic acute kidney injury (ATN). FENa < 1% suggests prerenal; > 2% suggests intrinsic AKI.

For educational and clinical reference. Not a substitute for medical judgment. See the medical disclaimer.
FENa
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Interpretation
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References

  1. Espinel CH. The FENa test. Use in the differential diagnosis of acute renal failure. JAMA. 1976;236(6):579-581.
  2. 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):2223-2229.

How to use

  1. Enter urine and plasma sodium and creatinine.
  2. FENa and interpretation update instantly.
  3. Use FEUrea instead if patient is on diuretics.

Frequently asked questions

What is FENa used for?

FENa helps differentiate prerenal AKI from intrinsic (ATN) AKI in oliguric patients.

How is FENa calculated?

FENa (%) = (Urine Na × Plasma Cr) / (Plasma Na × Urine Cr) × 100.

What thresholds matter?

FENa < 1% suggests prerenal AKI; FENa > 2% suggests intrinsic AKI (ATN). Values between 1–2% are indeterminate.

What limits FENa interpretation?

FENa is unreliable if the patient is on diuretics, has CKD, glycosuria, or contrast nephropathy. In those cases, FEUrea is preferred.

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