Acute Renal failure – working classification

Pre-renal

• Urinary sodium < 20 mmol/L
  • Fractional excretion of sodium (FeNa) << 1%
• Osmolality > 500 mosmol/kg
  • Urinary osmolality / Plasma osmolality > 1.5
    • i.e. high urinary creatinine and urea

Acute Tubular Necrosis (ATN)

• Urinary sodium > 40 mmol/L
  • FeNa > 1%
• Osmolality < 350 mosmol/kg
  • Ur osm / Pl osm < 1.5

Common Reversible Amplifiers of Chronic Renal Failure

• uncontrolled hypertension*
• obstruction / reflux
• infection
• analgesics / other nephrotoxics (e.g. gentamycin)
• calcium or urate deposits
• other factors promoting sustained increase in glomerular pressures and flows ⇒ scarring of remaining nephrons
  • high protein diet* → low protein diet
  • diabetes mellitus
  • severe anaemia
  • chronic renal vasodilator treatment
  • pregnancy

*factors which can influence the natural history of the disease