🫘 Fractional Excretion of Sodium (FENa)
Calculate the fractional excretion of sodium (FENa) to work up acute kidney injury.
Fractional Excretion of Sodium (FENa)
Urine sodium (mmol/L)
Plasma sodium (mmol/L)
Urine creatinine (mg/dL)
Plasma creatinine (mg/dL)
When to use
Differentiate pre-renal from intrinsic (ATN) acute kidney injury.
How it works
FENa = (UNa × PCr) / (PNa × UCr) × 100. < 1% pre-renal; > 2% intrinsic/ATN.
Key points
- Unreliable after diuretics — use FEUrea instead.
- Also unreliable in CKD, contrast nephropathy and glomerulonephritis.
- Interpret with the clinical picture and urine microscopy.
References
Decision support for licensed clinicians only; not a substitute for clinical judgement, diagnosis or local protocols.