Fractional Excretion of Sodium (FENa) Calculator

The Fractional Excretion of Sodium Calculation (FENa) requires the following patient parameters : Plasma Sodium and Urine Sodium in mEq/L. Plasma Creatinine and Urine Creatinine in mg/dL.

FeNA calculator (#16)

Formula for FENa in  % =  [(PCr × UNa ) / (PNa × UCr)] x 100

PCr plasma creatinine, UNa urine sodium, PNa plasma sodium, and UCr urine creatinine

Interpretation of FENa

Renal handling of sodium (filtered sodium) provides supportive information about the possible etiology of acute kidney injury.

FENa valueUNa (mmol/L)Cause of renal injuryEtiology
<1%<20Pre-renal AKI1. Congestive heart failure
2. Renal Artery Stenosis
3. Septic Shock
4. Hypovolemia
5. Hepatorenal syndrome
1-4%>40Intrinsic renal injury1. Acute Tubular Necrosis
2. Acute interstitial nephritis
3. Glomerulonephritis
>4%>40Post-renal AKIObstructive uropathy (ureteric urolithiasis, benign prostatic hyperplasia)

AKI Acute Kidney Injury, UNa Spot urine Sodium


This calculator is used for distinguishing between the various causes of AKI (pre-renal, post-renal, or intrinsic/renal causes).


FENa estimation is likely to be inaccurate in the setting of uncontrolled glucosuria (diabetes mellitus), concomitant diuretic exposure, known chronic kidney disease, or known obstructive uropathy. For patients taking diuretics, fractional excretion of urea is recommended. This is due to the natriuresis induced by diuretics.


Post published on February 5, 2022 and Last Updated on March 16, 2023 by MyEndoConsult

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