What is the normal level of the serum potassium?

3.5–5.0 mmol/l.

What is the distribution of potassium in the body?

98% of the total body potassium is intracellular. The intracellular concentration is ∼150 mmol/l compared to ∼4 mmol/l in the serum.

How is potassium regulated?

There are a number of influential factors on serum potassium

Dietary potassium: the ‘Western’ diet may contain 20–100 mmol of potassium daily

Aldosterone: this is a mineralocorticoid steroid hormone produced by the zona glomerulosa of the adrenal cortex. It stimulates sodium reabsorption in the distal convoluted tubule and cortical collecting duct through an active exchange with potassium, whose excretion is therefore promoted

Acid-Base balance: potassium and H+ are exchanged at the cell membrane, so that excess of one or the other leads to increased exchange. Thus, acidosis leads to hyperkalaemia and vice versa. Similarly, alkalosis can lead to hypokalaemia and vice versa. This also occurs at the kidney where reabsorption of one causes excretion of the other

Tubular fluid flow rate: increased flow rate promotes potassium secretion. This is one method by which some diuretics may cause hypokalaemia

Insulin: this stimulates potassium uptake into cells, reducing the serum level

What are the causes of hyperkalaemia?

Artefact: haemolysis in the blood bottle

Excess oral or i.v. administration

Redistribution:

Between the ICF and ECF due to injury: intravascular haemolysis, burns, tissue necrosis

Reduced cellular uptake: insulin deficiency, acidosis

Decreased excretion:

Renal origin: renal failure, potassium-sparing diuretics

Adrenal origin: Addison's disease

Mineralocorticoid resistance: systemic lupus erythematosus, chronic interstitial nephritis