Evaluation of Volume Status

FENa

  • FENa = (Urine Na/Plasma Na)/(Urine Cr/Plasma Cr) x 100
    • FENa <1%: Pre-Renal/Hepatorenal
    • FENa >1%: Renal (ATN, etc)
    • FENa is less accurate without oliguria
    • In presence of met alkalosis, urinary Cl is more accurate indicator of volume status than urinary Na
    • Some cases of contrast-induced and rhabdo-related ATN may have low FENa

FE Urea

  • FE Urea = Urine Urea/Plasma Urea)/(Urine Cr/Plasma Cr)
    • FE Urea <35%: Pre-Renal/Hepatorenal

References

  • Carvounis CP, Nisar S, Guro-Razuman S. Significance of the fractional excretion of urea in the differential diagnosis of acute renal failure. Kidney Int 2002; 62:2223-2229
  • Kaplan AA, Kohn OF. Fractional excretion of urea as a guide to renal dysfunction. Am J Nephrol 1992; 12:49-54