Fractional Excretion of Sodium (FENa)
Distinguishes pre-renal from intrinsic renal AKI using urine and serum sodium and creatinine.
Score interpretation
FENa < 1%: Consistent with pre-renal AKI (avid sodium retention). Kidney is trying to preserve volume.
→ IV fluid resuscitation (250–500 ml crystalloid challenge). Monitor urine output. Note: FENa < 1% also seen in contrast nephropathy, myoglobinuria, and early obstruction.
FENa 1–2%: Indeterminate. May be pre-renal or intrinsic renal.
→ Clinical context essential. Consider FeUrea if diuretics given.
FENa > 2%: Consistent with intrinsic renal AKI (ATN). Kidney unable to conserve sodium.
→ Consider: ATN (ischaemic/nephrotoxic), acute interstitial nephritis, glomerulonephritis. Cautious fluids only. Nephrology review. Stop nephrotoxins.
Interpretation bands for the FENa. Apply clinical judgement and local guidance.
References
- Espinel CH. The FENa test. Use in the differential diagnosis of acute renal failure. JAMA. 1976.
Related
Curated clinical cross-links plus same-class fallbacks.
- Mannitol (Osmotic Diuretic — Renal/Neurological) · Acute Oliguric Renal Failure / Raised ICP
- Thiopental Sodium · Barbiturate Induction Agent
- Sodium Bicarbonate · Alkalising Agent / Electrolyte
- Sodium Chloride 3% (Hypertonic Saline) · Hypertonic Electrolyte Solution — ICP/Hyponatraemia Management
- Sodium Nitroprusside · Vasodilator — Nitric Oxide Donor (IV)
- Dantrolene sodium · Skeletal muscle relaxant (RyR1 inhibitor)
- Difficult Airway Algorithm (DAS) · DAS 2015; Royal College of Anaesthetists
- Major Haemorrhage Protocol · NICE NG24; UK MHP guidelines
- New-Onset Atrial Fibrillation · ESC 2020 AF Guidelines; NICE NG196
- Hypertensive Emergency · ESC/ESH 2018 Hypertension Guidelines; NICE NG136
- Bradycardia Management · Resuscitation Council UK ABCDE; ESC 2021 Pacing Guidelines
- Ventricular Tachycardia / Fibrillation · Resuscitation Council UK ACLS; ESC 2022 Ventricular Arrhythmia Guidelines
Decision support only — verify against a current formulary, NICE, or your local guideline before clinical use.