Fractional Excretion of Sodium (FENa)
Do not use in patients taking diuretics or with known chronic kidney disease, urinary tract obstruction, or acute glomerular disease. Use FEUrea in patients on diuretics.
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- No FENa percentage will always accurately suggest “pre-renal” disease. Always consider history, clinical context, physical exam, and current medications.
- Obtaining repeat FENa or urine studies throughout a patient’s hospital course can give more clinical clues.
- Non-volume depleted states with low urine sodium (and consequently low FENa) include: acute glomerulonephritis, cardiorenal syndrome, hepatorenal syndrome, contrast-related nephropathy, and rarely, acute obstruction and early acute interstitial nephritis (AIN) or acute tubular necrosis (ATN).
Some experts recommend placing a Foley catheter in all patients with acute renal failure to remove obstructive uropathy from the differential regardless of the FENa, especially in patients who are unable to provide information about their bladder and urination.
- Devika Nair, MD