Contents

Search

fractional excretion of sodium (FENA)

Defined as: excreted Na+/filtered Na+ Indications: - acute renal failure - prerenal azotemia - acute tubular necrosis - obstructive uropathy Procedure: Measured as: (urine Na+/serum Na+) / (urine creatinine/serum creatinine) Clinical significance: Useful for distinguishing prerenal from acute tubular necrosis or post-renal obstruction as etiology of acute renal failure (ARF): FENA renal disease - < 1% prerenal vs glomerulophritis* - > 1% renal or post-renal# * diuretic use may result in a high FENA with prerenal azotemia; for these patients, fractional excretion of urea may be helpful # in early obstructive uropathy, FENA may be low FENA < 1% 1) urinalysis: benign urine -> prerenal azotemia 2) urinalysis: dysmorphic erythroctes, RBC casts -> glomerulonephritis FENA > 1% 1) urinalysis: muddy brown granular casts or tubular epithelial casts -> ATN 2) urinalysis: RBC, hemoglobinuria, urinary crystals -> obstructive uropathy

Related

fractional excretion of urea

General

urinary indices

References

  1. Saunders Manual of Medical Practice, Rakel (ed), WB Saunders, Philadelphia, 1996, pg 536-37
  2. Medical Knowledge Self Assessment Program (MKSAP) 11, 14, 16. American College of Physicians, Philadelphia 1998, 2006, 2012