Calcmedical

FENa (Fractional Excretion of Sodium)

NephrologyCritical Care

Medical context

Calculate fractional excretion of sodium to help differentiate prerenal from intrinsic AKI patterns.

Nephrology and medicine teams use this when interpreting renal function, electrolytes, or fluid plans.

This page explains the FENa formula, how to interpret the output, known limitations, and peer-reviewed references so you can verify results against primary sources and local protocols.

It is grouped under Nephrology because kidney function, electrolytes, and renal dosing helpers.

How to use this calculator

  1. Enter the values requested by the FENa calculator using the units shown beside each field.
  2. Review the calculated result and read the interpretation section before acting on the output.
  3. Check limitations and references if the result will change management, dosing, or disposition.
  4. Use the related calculators section when you need supporting values (for example electrolytes, weight, or complementary risk scores).

Calculator

Result

1.14%

Indeterminate — interpret clinically

Educational use only. Confirm results with clinical judgment, primary sources, and local protocols. Not a substitute for professional medical advice. Full disclaimer.

Formula

FENa (%) = (UNa/PNa) ÷ (UCr/PCr) × 100.

Interpretation

In oliguric AKI, FENa <1% often suggests prerenal physiology; >2% often suggests ATN — many exceptions.

Limitations

Diuretics, CKD, contrast, and sepsis confound FENa. Not definitive alone.

Frequently asked questions

Can I use FENa on diuretics?
Loop diuretics raise FENa; consider FEUrea or clinical context instead.
Is the FENa result enough to make a treatment decision?
No. Calculators support medical decision-making but do not replace examination, shared decision-making, institutional protocols, or consultant input when stakes are high.
Does Calcmedical store the values I type in?
Inputs are processed in your browser for this session. We do not ask for patient names or medical record numbers. See our privacy policy for hosting and analytics details.

References

  • Classic FENa literature in AKI