Fractional Excretion of Sodium measures the percentage of filtered sodium that is excreted. Helps differentiate prerenal AKI ( 2%).

When is FENa unreliable?

On diuretics (use FEUrea instead), contrast nephropathy, early obstruction, myoglobinuria, acute GN. Also unreliable in CKD baseline.

What are the cutoffs?

2%: Intrinsic renal (ATN, AIN). >4%: Strongly suggests ATN.

What values do I need?

Serum Na, Serum Cr, Urine Na, Urine Cr. All from same time point. Serum and urine samples should be collected together.

FEUrea < 35% suggests prerenal. More reliable than FENa in patients on diuretics. Calculate: (Urine Urea × Serum Cr) / (Serum Urea × Urine Cr) × 100.

FENa Calculator

Q: What about FEUrea?

FEUrea < 35% suggests prerenal. More reliable than FENa in patients on diuretics. Calculate: (Urine Urea × Serum Cr) / (Serum Urea × Urine Cr) × 100.

Fractional Excretion of Sodium for AKI evaluation.

Serum Values

Serum Sodium

mEq/L

Serum Creatinine

mg/dL

Urine Values

Urine Sodium

mEq/L

Urine Creatinine

mg/dL

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FENa

0.00 %

Prerenal AKI

Fluid responsive. Consider volume resuscitation.

Formula

FENa = (UNa × SCr) / (SNa × UCr) × 100

= (15 × 2) / (140 × 80) × 100 = 0.00%

Reference

<1%: Prerenal

1-2%: Indeterminate

>2%: Intrinsic

Frequently Asked Questions

About the FeNa Calculator

What it calculates

This fena calculator applies a validated clinical scoring method used in healthcare settings. Fractional excretion of sodium.

When to use it

Use as a clinical decision support aid alongside professional judgment — not as a standalone diagnosis.

Example

Adjust the inputs above to model your specific scenario with the FeNa Calculator.

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FENa Calculator

Serum Values

Urine Values

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0.00 %

Prerenal AKI

Formula

Reference

About the FeNa Calculator

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