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Fractional excretion of sodium (FENa)

Measures the proportion of filtered sodium excreted in urine. In oliguric AKI it helps distinguish prerenal azotemia (intact sodium-retaining tubules) from acute tubular necrosis.

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Method · Limits of application

FENa/Espinel 1976; Miller 1978, 100×UNa×PCr/(PNa×UCr); simultaneous samples

Miller’s 1978 evidence concerns acute oliguria and showed that urinary indices do not always separate prerenal causes from tubular necrosis. The result alone does not establish the cause of renal dysfunction. Clinical conditions, sample timing and medications must be considered according to the source of the version used.

Conditions of use

Check the population, units, inclusion and exclusion criteria, and version in the original source. A result alone does not establish a diagnosis, discharge decision or prescription.

Documented parameters

Urine sodium · mEq/L
Serum sodium · mEq/L
Urine creatinine · mg/dL
Serum creatinine · mg/dL
Diuretic use in the last 24 h?

3/3 reference cases checked. Numerical tests are not clinical validation.

Sources and documentation

Documented formula

Transcribed from the source or a recorded revision; this is not a clinical recommendation.

FENa (%) = (urine Na × serum creatinine) ÷ (serum Na × urine creatinine) × 100.

Use urine and blood collected at the same time, before diuretics or fluid administration whenever possible.

References

Identifier: fracao-de-excrecao-de-sodio

Original clinical content: Brazilian Portuguese.

Method version

FENa/Espinel 1976; Miller 1978, 100×UNa×PCr/(PNa×UCr); simultaneous samples

fracao-de-excrecao-de-sodio@native-2026-10-04+0e50f6e4a6a0

Source for the active edition

The bibliographic edition identifies the source. By itself, it proves neither full conformity of the formula nor clinical approval.

Synthetic cases checked (3)

Synthetic cases for checking the implementation, with no patient data.

Case 1

reference-001

Inputs

Urine sodium: 10 mEq/L
Serum sodium: 140 mEq/L
Urine creatinine: 100 mg/dL
Serum creatinine: 2 mg/dL
Diuretic use in the last 24 h?: No

{
  "una": 10,
  "pna": 140,
  "ucr": 100,
  "pcr": 2,
  "diuretico": "0"
}

Expected result

{
  "fena": 0.1429
}

Actual result

{
  "fena": 0.14285714285714285
}

Case 2

reference-002

Inputs

Urine sodium: 35 mEq/L
Serum sodium: 140 mEq/L
Urine creatinine: 50 mg/dL
Serum creatinine: 2 mg/dL
Diuretic use in the last 24 h?: No

{
  "una": 35,
  "pna": 140,
  "ucr": 50,
  "pcr": 2,
  "diuretico": "0"
}

Expected result

{
  "fena": 1
}

Actual result

{
  "fena": 1
}

Case 3

reference-003

Inputs

Urine sodium: 60 mEq/L
Serum sodium: 135 mEq/L
Urine creatinine: 40 mg/dL
Serum creatinine: 4 mg/dL
Diuretic use in the last 24 h?: Yes

{
  "una": 60,
  "pna": 135,
  "ucr": 40,
  "pcr": 4,
  "diuretico": "1"
}

Expected result

{
  "fena": 4.444
}

Actual result

{
  "fena": 4.444444444444445
}

Code and reproducibility

This tool’s code on GitHub

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Sources, version and reproduction instructions

The code tests are technical checks. Clinical approval and professional translation review are recorded separately.

Relationship with cancer research

General context — relationship to be defined

A resource for general clinical contexts. This edition does not assign a specific oncological relationship; selecting it for a study requires a justified question, population and purpose.