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Example One

  • ↑Na+
  • ↔K+
  • ↑↑Urea
  • ↑↑Creatinine
Renal failure
Main causes of chronic renal failure:


Massively raised urea and creatinine together can only be caused by renal failure.
  • Metabolism of urea – urea comes from CO2 and NH2. NH2 comes from protein. Thus, to have a high urea, you either have to have renal failure, or excessive protein load. The creatinine then tells you which it is; ↑↑creatinine and ↑↑urea will be renal failure, ↑↑urea and ↔creatinine will just be patients with a high protein load.
  • What causes a high protein load? – think of situations where the body utilises protein instead of carbohydrate as its main energy source. i.e. starvation, (usually alcoholism), or extreme exercise (athletes). Also, there are other situations where there are excessive amounts of protein in the blood: haematemesis, and liver failure.

Example two

  • ↑Na+
  • ↓K+
  • ↔Urea
  • ↔Creatinine
Associated symptoms
  • hypertension
Likely diagnosis
Hyperaldosteronism (Conn’s Syndrome)


Creatinine and urea are normal, thus it is unlikely to be kidney disease.
Aldosterone causes the retention of sodium at the expense of potassium. It acts on the PCT causing the synthesis of more Na+/K+ exchange channels. Thus, in thepresence of excess of aldosterone there will be excess secretion of K+, and retention of Na+. The retention of Na+ will cause a secondary retention of water, resulting in hypertension.


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