Nephrology
Fractional Excretion of Sodium (FENa)
Differentiates pre-renal AKI from intrinsic.
Fractional Excretion of Sodium (FENa) calculator
Result
0.3%
< 1% — Pre-renal (avid Na reabsorption)
Unreliable if diuretics given. Use FEUrea if on diuretics.
How to use it
- 1
Spot urine and serum at same time. Collect both samples simultaneously for accuracy.
- 2
FENa formula. FENa% = (UNa × PCr) / (PNa × UCr) × 100.
- 3
Diuretics confound FENa. Furosemide ↑ urine Na → falsely high FENa. Use FEUrea instead.
When to use it
- AKI work-up without diuretics
- Classic use: oliguria, ↑ creatinine — is this pre-renal or ATN?
- Not useful in CKD
- CKD patients often spill more Na; FENa less discriminating.
- Heart failure and hepatorenal
- FENa < 1% in HRS despite ATN-like picture — use clinical context.
A reference for clinicians and students, not medical advice. A score supports a decision; it does not make one. Check every result against the patient in front of you and your local protocol.
At a glance
- Specialty
- Nephrology
- Inputs
- 4
- Type
- Formula
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