Fractional Excretion of Sodium
Separates prerenal from intrinsic acute kidney injury using sodium excretion.
When to use
Oliguric acute kidney injury in adults when trying to distinguish prerenal from intrinsic causes.
Pearls and pitfalls
- FENa compares sodium excretion with creatinine excretion, correcting for plasma concentration.
- Diuretics, osmotic diuresis and chronic kidney disease can raise FENa and mimic a nonprerenal pattern.
- Fractional urea excretion can be useful when the patient uses diuretics.
- The result is supportive; volume status, urine sediment and response to replacement remain central.
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Formula
FENa (%) = (urine sodium × plasma creatinine) / (plasma sodium × urine creatinine) × 100.
Evidence
Index derived to differentiate prerenal acute kidney injury from acute tubular necrosis in paired blood and urine samples.
References
- Espinel CH. The FENa test. Use in the differential diagnosis of acute renal failure. JAMA. 1976;236(6):579-581. doi:10.1001/jama.236.6.579
Frequently asked questions
What is Fractional Excretion of Sodium?
Separates prerenal from intrinsic acute kidney injury using sodium excretion. Oliguric acute kidney injury in adults when trying to distinguish prerenal from intrinsic causes.
How is the result calculated?
FENa (%) = (urine sodium × plasma creatinine) / (plasma sodium × urine creatinine) × 100.
How should the result be interpreted?
Index derived to differentiate prerenal acute kidney injury from acute tubular necrosis in paired blood and urine samples.
What are the sources?
Espinel CH. The FENa test. Use in the differential diagnosis of acute renal failure. JAMA. 1976;236(6):579-581.