FENa Calculator — Fractional Excretion of Sodium
Compute the fractional excretion of sodium (FENa) to help separate pre-renal acute kidney injury from intrinsic tubular injury (acute tubular necrosis).
When to use it
In selected oliguric AKI, FENa below 1% suggests sodium avidity and above 2% may support tubular injury. CKD, diuretics, sepsis and several intrinsic kidney diseases limit discrimination. FEurea is also imperfect; neither result establishes the cause of AKI.
Formula
FENa (percent) = (urine sodium x plasma creatinine) / (plasma sodium x urine creatinine) x 100.
Category
Acute Kidney Injury
References
- Espinel CH. The FENa test. Use in the differential diagnosis of acute renal failure. JAMA. 1976;236:579-81. PMID: 947239
- Steiner RW. Interpreting the fractional excretion of sodium. Am J Med. 1984;77:699-702. PMID: 6486145
- Abdelhafez M et al. Diagnostic Performance of Fractional Excretion of Sodium for the Differential Diagnosis of Acute Kidney Injury: A Systematic Review and Meta-Analysis. Clin J Am Soc Nephrol. 2022;17:785-797. PMID: 35545442
About NephroMind
This calculator is part of NephroMind, a free clinical decision-aid platform from the Arab Society of Nephrology and Renal Transplantation (ASNRT) — over 128 bedside nephrology calculators plus a renal drug-dosing database, coded by a practicing transplant nephrologist.