Nephrology Equation Moderate evidence Clinical review pending v1.0.0

Fractional Excretion of Sodium (FENa)

Is oliguric acute kidney injury more likely prerenal or intrinsic?

Add to favourites

Calculator

Fields marked * are required. Units can be changed per field.

Your result will appear here

Complete the inputs and select Calculate. Results update instantly for point scores.

About this tool

Percentage of filtered sodium excreted in urine, used to differentiate prerenal azotaemia from ATN.

Intended use

Adults with oliguric AKI not receiving diuretics.

Outcome

Physiological classification of AKI

Time horizon

Point in time

Derivation population

Small physiological studies in oliguric AKI.

Limitations

Unreliable with diuretics, CKD and several AKI causes.
Best evidence in oliguric patients.

Clinical problems

Kidney function and AKI

Evidence

Evidence level

Moderate evidence

Physiological index; thresholds from small studies. Methodology

Evidence summaries for this tool are awaiting independent clinical review. Statistics are shown only where they could be attributed to a specific publication.

References

Original publicationEspinel CH. The FENa test. Use in the differential diagnosis of acute renal failure. JAMA 1976;236:579-581. Find on PubMed (opens in a new tab)
Validation studyMiller TR, Anderson RJ, Linas SL, et al. Urinary diagnostic indices in acute renal failure: a prospective study. Ann Intern Med 1978;89:47-50. Find on PubMed (opens in a new tab)

Version history

Version	Formula	Effective	Reviewer	Changes
v1.0.0	Standard FE formula	2026-10-03	—	Initial implementation with reference test vectors.

Related tools

Nephrology · Equation

Cockcroft-Gault

What is the estimated creatinine clearance for drug dosing?

Moderate evidence Point in time Nephrology · Equation

FEUrea

Is AKI prerenal in a patient receiving diuretics?

Limited evidence Point in time Nephrology · Equation

KFRE

What is the 2- and 5-year risk of kidney failure in CKD G3–G5?

Strong evidence 2 and 5 years Nephrology · Equation

CKD-EPI 2021

What is the estimated glomerular filtration rate?

Strong evidence Point in time

Clinical decision support only. Interpret results in the context of the individual patient and current guidance; HumanPulse does not replace professional medical judgment.