FENa fração excreção Na
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
About this calculator
The Sodium Excretion Fraction (FENa) calculator helps assess kidney function in cases of suspected acute kidney injury. The formula used is (UNa × Cr_s) / (Na_s × UCr) × 100, where UNa is urinary sodium, Cr_s is serum creatinine, Na_s is serum sodium, and UCr is urinary creatinine. The result differentiates pre-renal causes (insufficient blood flow to kidneys) from intrinsic kidney damage.
Typically, FENa is low (<1%) in pre-renal conditions like dehydration or shock, and high (>3%) in intrinsic kidney damage, such as acute tubular necrosis. This tool is often used alongside serum creatinine levels and urine output for accurate evaluation. A nephrologist should interpret the results to ensure proper diagnosis.
Factors like recent diuretic use, fluid intake, and chronic conditions can affect FENa. It does not replace a comprehensive clinical assessment. Patients with a history of kidney disease or hypertension should consult a specialist before self-interpreting results.
Frequently asked questions
What is Sodium Excretion Fraction (FENa)?
It is a calculation that helps differentiate pre-renal and intrinsic causes of acute kidney injury by comparing urinary sodium excretion to serum sodium levels.
What are normal FENa values?
Values below 1% suggest pre-renal causes; above 3% indicate intrinsic kidney damage. Between 1%, 3%, results are inconclusive and require further tests.
When should this calculator be used?
For patients with suspected acute kidney injury, particularly to distinguish between reduced kidney perfusion and direct kidney damage.
Do diuretics affect the result?
Yes, diuretics can lower FENa, potentially masking the diagnosis. Inform your doctor about any medications you're taking.