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FeNa Calculator

Calculate the Fractional Excretion of Sodium (FeNa) to differentiate between pre-renal and intrinsic acute kidney injury.

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Formula

(UNa * SCr) / (SNa * UCr) * 100

Measures the percentage of sodium filtered by the kidney that is excreted in the urine.

Worked Example

Serum: Na 140, Cr 1.5; Urine: Na 10, Cr 50 -> FeNa ~ 0.14%.

Frequently Asked Questions

What does a FeNa < 1% mean?

A FeNa below 1% suggests a pre-renal cause (like dehydration), where the kidneys are aggressively reabsorbing sodium.

What does a FeNa > 2% mean?

A FeNa above 2% suggests intrinsic renal damage, such as Acute Tubular Necrosis (ATN).

Can diuretics affect FeNa?

Yes. Diuretics increase sodium excretion, which can make a pre-renal state look like an intrinsic one. In such cases, the Fractional Excretion of Urea (FeUrea) is often used instead.

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