Causes of a raised urea

Pre-renal:

• increased hepatic production of urea:
  • high protein diet
  • gastro-intestinal haemorrhage - "protein meal"
  • increased protein catabolism - trauma, major surgery, extreme starvation with muscle breakdown
• increased renal reabsorption of urea - any cause of reduced renal perfusion, for example, congestive cardiac failure, shock, severe diarrhoea
• iatrogenic - urea infusion for it's diuretic action, drug therapy leading to an increased production e.g. tetracyclines, corticosteroid

Renal:

• any cause of acute or chronic renal failure

Post-renal:

• any cause of urinary outflow obstruction