- 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
- any cause of acute or chronic renal failure
- any cause of urinary outflow obstruction