Urinary diagnostic indices in acute renal failure: a prospective study

Ann Intern Med. 1978 Jul;89(1):47-50. doi: 10.7326/0003-4819-89-1-47.


A prospective analysis of the value of urinary diagnostic indices in ascertaining the cause of acute renal failure was undertaken. Our results show that in the setting of acute oliguria a diagnosis of potentially reversible prerenal azotemia is likely with urine osmolality greater than 500 mosm/kg H2O, urine sodium concentration less than 20 meq/litre, urine/plasma urea nitrogen ratio greater than 8, and urine/plasma creatinine ratio greater than 40. Conversely, a urine osmolality less than 350 mosm/kg, urine sodium concentration greater than 40 meq/liter, urine/plasma urea nitrogen ratio less than 3, and urine/plasma creatinine ratio less than 20 suggest acute tubular necrosis. A significant number of oliguric patients will not have urinary indices that fall within these guidelines. In this setting, urine sodium concentration divided by the urine-to-plasma creatinine ratio (the renal failure index) and the fractional excretion of filtered sodium provide a reliable means of differentiating reversible prerenal azotemia from acute tubular necrosis.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acute Kidney Injury / diagnosis
  • Acute Kidney Injury / urine*
  • Aged
  • Creatinine / metabolism
  • Female
  • Humans
  • Kidney Tubular Necrosis, Acute / urine
  • Male
  • Middle Aged
  • Osmolar Concentration
  • Prospective Studies
  • Sodium / urine
  • Urea / metabolism
  • Uremia / urine


  • Urea
  • Sodium
  • Creatinine