Renal & Electrolytes

Fractional Excretion of Sodium (FENa) Calculator

Share of filtered sodium the kidney lets go; under 1% suggests a prerenal state, over 2% tubular injury, unless diuretics have been given.

Reviewed by Alex G, BSN, RN, CEN, CCRN, CMC, NREMT-P · From the Reference tab of the app

Turn on JavaScript to use this calculator, or open it in the web app.

Formula

FENa = (Urine Na × Serum Cr) / (Serum Na × Urine Cr) × 100

How it is used

• FENa < 1%: Suggests Pre-renal AKI (hypovolemia, poor perfusion). Kidneys are holding onto sodium.
• FENa > 2%: Suggests Intrinsic AKI (Acute Tubular Necrosis). Kidneys are wasting sodium.

Key points

• FENa is inaccurate in patients taking diuretics. Use Fractional Excretion of Urea (FEUrea) instead.

Same formula as the app. Open it in the web app.

Related one-pagers

• Acute Kidney InjuryFENa · <1% · >2%
• Electrolyte Imbalances
• ABG Interpretation in 6 Steps
• CRRT (Continuous Renal Replacement)

Related calculators

• Anion Gap
• BUN/Cr Ratio
• Corrected Calcium
• Corrected Sodium (Hyperglycemia)
• Creatinine Clearance (Cockcroft-Gault)
• CRRT Effluent Dose (mL/kg/h)
• Fractional Excretion of Urea (FEUrea)
• Free Water Deficit

For education and exam preparation only. Follow your institution’s protocols. For education and exam preparation only. Verify results independently and follow your institution’s protocols. Not a substitute for clinical judgment.