What does FENa measure?

FENa estimates the percentage of filtered sodium that is excreted in the urine.

What does a FENa below 1% suggest?

In oliguric acute kidney injury, a value below 1% is consistent with prerenal azotemia or another sodium-avid state.

Can diuretics affect FENa interpretation?

Yes. Diuretics can make FENa unreliable; FEUrea may be considered instead, with a value below 35% often used in this context.

Is this calculator medical advice?

No. FENa should be interpreted by a qualified clinician with the complete clinical picture.

Elysia Tools

Navigation

Health

Fractional Excretion of Sodium (FENa)

Calculate the Fractional Excretion of Sodium (FENa) to differentiate prerenal from intrinsic acute kidney injury: FENa (%) = [U_Na × S_Cr] / [S_Na × U_Cr] × 100. In oliguric AKI, FENa <1% suggests prerenal azotemia (sodium-avid state: volume depletion, heart failure, hepatorenal syndrome), while FENa ≥1% suggests intrinsic injury (typically ATN). FENa >4% is sometimes cited as supportive of post-obstructive pathology. Caveats: unreliable on diuretics (use FEUrea <35%), contrast/sepsis ATN can present with low FENa, chronic CKD and glucosuria elevate FENa independently. Derived from Espinel CH, JAMA 1976. Most useful in oliguric AKI; interpret with full clinical context. Not medical advice.

Execution

Run this tool

Fill in the form, run the tool, and review the result in one place.

Prepared example runs

Click an example to fill the form automatically. File inputs still need an upload.

2 examples

U_Na=20, S_Cr=1.5, S_Na=140, U_Cr=120 → FENa = 0.1786% (prerenal)

FENa = (20×1.5)/(140×120)×100 = 0.1786%. Below 1% — consistent with prerenal azotemia (sodium-avid state).

{"result":"FENa = 0.1786% (< 1% — Consistent with prerenal azotemia). Method: FENa = (U_Na·S_Cr)/(S_Na·U_Cr)·100.","metadata":{"input":{"urineSodium":20,"serumCreatinine":1.5,"serumSodium":140,"urineCreatinine":120},"result":{"fena":0.1786,"unit":"%","category":"< 1%","interpretation":"Consistent with prerenal azotemia (sodium-avid state). Consider volume depletion, heart failure, hepatorenal syndrome. Caution: contrast/sepsis ATN and diuretics can also yield low FENa.","method":"FENa = (U_Na·S_Cr)/(S_Na·U_Cr)·100","model":"Espinel CH. JAMA 1976;236(6):579-581. Most useful in oliguric AKI. Not medical advice."}}}

U_Na=60, S_Cr=2.0, S_Na=135, U_Cr=60 → FENa = 1.4815% (intrinsic/ATN)

FENa = (60×2.0)/(135×60)×100 = 1.4815%. At least 1% — consistent with intrinsic renal injury, typically acute tubular necrosis (ATN).

{"result":"FENa = 1.4815% (1–4% — Consistent with intrinsic renal injury, typically ATN). Method: FENa = (U_Na·S_Cr)/(S_Na·U_Cr)·100.","metadata":{"input":{"urineSodium":60,"serumCreatinine":2,"serumSodium":135,"urineCreatinine":60},"result":{"fena":1.4815,"unit":"%","category":"1–4%","interpretation":"Consistent with intrinsic renal injury, typically acute tubular necrosis (ATN). Damaged tubules cannot reabsorb sodium effectively.","method":"FENa = (U_Na·S_Cr)/(S_Na·U_Cr)·100","model":"Espinel CH. JAMA 1976;236(6):579-581. Most useful in oliguric AKI. Not medical advice."}}}

Inputs

Set the required fields, then run the tool.

5 options

SettingsAdjust formats, ranges, numbers, and modes.5

Urine Sodium U_Na (mmol/L)numberRequiredUrine sodium concentration in mmol/L. Must be ≥0.Serum Creatinine S_Cr (mg/dL)numberRequiredSerum creatinine in mg/dL. Must be positive.Serum Sodium S_Na (mmol/L)numberRequiredSerum sodium concentration in mmol/L. Must be positive.Urine Creatinine U_Cr (mg/dL)numberRequiredUrine creatinine concentration in mg/dL. Must be positive.Decimal PlacesnumberOptional

Result

Ready for a run

Run the tool to preview files, text, structured data, or streamed output here.

Samples

Fractional Excretion of Sodium (FENa)

Run this tool

Prepared example runs

Inputs

Result

Examples that match this tool

Continue with connected tools and hubs

Prepared example runs

Inputs

Result

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Overview

When to use

How it works

Use cases

Examples

1. Low FENa consistent with prerenal azotemia

2. FENa in the intrinsic injury range

FAQ

Web Image Processing Python Samples

Android Image Processing Java Samples

Android Image Processing Kotlin Samples

SVG Samples

Twitter / X Thread Splitter

Words to Number

Batch Image Watermark

AHU Coil Capacity Calculator (Cooling / Heating)

Kidney Function, Dialysis, and Renal Dose Calculators

Text Case, Encoding, and Normalization Conversion Tools

Text Tools

Text Analysis, Readability, and Content Inspection Tools