Fractional Excretion of Sodium (FeNa)

Calculates FeNa as a context-dependent physiologic clue in AKI; it can support but does not by itself distinguish hemodynamic/prerenal physiology from intrinsic kidney injury.

Formula

FeNa = (Urine Na × Plasma Cr) / (Plasma Na × Urine Cr) × 100

Urine sodium (mEq/L)Plasma creatinine (mg/dL)Plasma sodium (mEq/L)Urine creatinine (mg/dL)

Result

Enter all values to see the result.

Limitations

Loop/thiazide diuretics can increase urine sodium and reduce FeNa's diagnostic usefulness; this makes interpretation less reliable rather than mathematically invalidating the calculation.
Less reliable in patients with underlying chronic kidney disease, contrast-induced nephropathy, or certain glomerulonephritides, which can show a low FeNa despite intrinsic injury.
A single value is a probabilistic aid, not a definitive diagnostic test — it should be interpreted alongside the full clinical picture, not in isolation.

References

Standard fractional-excretion formula; use only as an adjunct to hemodynamics, urine sediment, obstruction assessment and clinical trajectory.

Clinical Context & Relevant Topics (2)

Disease Reference

Acute Kidney Injury in Critical Care

Sepsis-AKI microcirculatory decoupling, KDIGO staging, Furosemide Stress Test (FST), urine microscopy, and the AEIOU dialysis threshold framework.

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Continuous Renal Replacement Therapy (CRRT)

Principles of convection vs diffusion, filtration fraction, delivered effluent dosing (20–25 mL/kg/h), Regional Citrate Anticoagulation, and citrate toxicity.

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Relevant Clinical Pathways (8)

Decision Protocols

Renal Replacement Therapy & CRRT Initiation

From urgent 'AEIOU' indication screening and modality selection to vascular access, dosing, and anticoagulation.

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Severe Hyperkalemia Emergency Management

From emergent cardiac membrane stabilization to intracellular shifting, elimination, and dialysis triggers.

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