fractional excretion of urea

Introduction

Defined as: excreted urea/filtered urea

Indications

• evaluation of prerenal azotemia in patients on diuretics

Clinical significance

• useful for assessing prerenal azotemia in patients with FENA > 1% & on a diuretic (FENA can be elevated by diuretics)
• fractional excretion of urea is less influenzed by diuretics than FENA
• a value of < 35% for fractional excretion of urea is consistent with prerenal azotemia

Procedure

Measured as:

 (urine urea/serum urea) / (urine creatinine/serum creatinine)

More general terms

• urinary indices

Additional terms

• fractional excretion of sodium (FENA)
• urea (carbamide)