Potassium is the predominant intracellular cation. This means that serum potassium concentrations are a poor indicator of total body potassium, as only 2% exists in the extracellular fluid. It is disturbances in the balance between the extracellular and intracellular concentrations that cause raised serum potassium levels, which may even occur when the total body potassium is low. As the patient has a serum potassium level of 6.6mmol/L, which is far higher than the upper limit of the reference range (3.3 - 4.7 mmol/L) it appears the patient is hyperkalaemic. The distribution of potassium in the body is about 150mmol/L in the intracellular fluid (ICF), and about 4mmol/L in the extracellular fluid (ECF). The ICF concentration is determined by the movement of cations across the cell membrane, so anything causing movement of potassium out of the cell will result in hyperkalaemia. The ECF concentration is determined by intake and excretion of potassium. In normal non-diseased individuals the amount of dietary potassium is equal to the amount excre

Smith, A.F. Beckett, G.J. Walker, S.W. Rae, P.W.H. (1998) Lecture Notes on Clinical Biochemistry. 6th edition. Blackwell science.

ted in the urine via the kidneys. This is normally between about 20-100mmol daily, but even potassium intake exceeding 100mmol will rarely result in hyperkalaemia as healthy kidneys can cope with excretion of high potassium loads, so a dietary excess rarely causes hyperkalaemia.

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