🫘 Fractional Excretion of Sodium (FENa)
Calculate the fractional excretion of sodium (FENa) to work up acute kidney injury.
Clinical takeaway
Unreliable after diuretics — use FEUrea instead.
Loading calculator…
Paste the link in Slack, Teams, X, or LinkedIn — the preview image comes from this page’s Open Graph card.
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.
Worked calculation
The values below come from this tool's own example placeholders and are computed server-side with the formula shown on this page, so the arithmetic can be checked quickly. It demonstrates how to substitute values only — it is not clinical advice and not a real case.
| Urine sodium | 20 mmol/L |
|---|---|
| Plasma sodium | 140 mmol/L |
| Urine creatinine | 100 mg/dL |
| Plasma creatinine | 2.0 mg/dL |
→FENa0.29%
- Interpretation：< 1% — suggests pre-renal
- Formula：FENa = (UNa·PCr)/(PNa·UCr) × 100
Frequently asked questions
- What is Fractional Excretion of Sodium (FENa)?
- Calculate the fractional excretion of sodium (FENa) to work up acute kidney injury.
- How is Fractional Excretion of Sodium (FENa) calculated? What is the core formula?
- FENa = (UNa × PCr) / (PNa × UCr) × 100. < 1% pre-renal; > 2% intrinsic/ATN.
- When is Fractional Excretion of Sodium (FENa) used?
- Differentiate pre-renal from intrinsic (ATN) acute kidney injury.
- What are the key clinical points for Fractional Excretion of Sodium (FENa)?
- Unreliable after diuretics — use FEUrea instead. Also unreliable in CKD, contrast nephropathy and glomerulonephritis. Interpret with the clinical picture and urine microscopy.
- What are the limits and cautions when using Fractional Excretion of Sodium (FENa)?
- For licensed clinicians and clinical researchers. Interpret results with history, investigations and local protocols; not a diagnosis or prescription, and not a substitute for multidisciplinary decision-making or local guidelines.
- How is Fractional Excretion of Sodium (FENa) calculated in practice? Can you show a worked example?
- Inputs: Urine sodium 20 mmol/L, Plasma sodium 140 mmol/L, Urine creatinine 100 mg/dL, Plasma creatinine 2.0 mg/dL → Result: FENa 0.29 %（Interpretation: < 1% — suggests pre-renal, Formula: FENa = (UNa·PCr)/(PNa·UCr) × 100）