5th April 2024

Hypokalaemia

This is defined as serum potassium levels of less than 3.5 mmol/L and can be divided into:

• Mild 3.1 – 3.5 mmol/L
• Moderate 2.5 – 3.0 mmol/L
• Severe < 2.5 mmol/L

The various mechanisms causing hypokalemia include: 

• Spurious hyperkalemia, where potassium is taken up by cells outside the body, e.g., white blood cells in leukaemia. This is likely to occur if there are delays in analysing the sample.
• Transcellular redistribution due to metabolic/respiratory alkalosis and in the presence of excess insulin levels
• Potassium depletion due to diuretic use, diarrhoea, laxative use/abuse and profuse sweating 
• Medications including beta adrenoreceptor agonists such as salbutamol and in theophylline overdose. 
• Hypomagnesaemia results in hypokalemia as reduced intracellular magnesium increases potassium secretion.
• Mineralocorticoid excess in primary hyperaldosteronism (Conn’s syndrome) and secondary hyperaldosteronism (renal artery stenosis).
• Bartter syndrome, where abnormal chloride ion transport in the loop of Henle results in sodium wasting, metabolic alkalosis and potassium depletion 
• Gitelman’s syndrome is the most common cause of congenital hypokalemia characterised by a defect in the distal tubule Na+/Cl– co-transporter gene. The result is hypokalemia, hypomagnesemia, metabolic alkalosis and hypocalciuria. Both Bartter and Gitelman’s syndrome activate the renin-angiotensin aldosterone system. 
• Vomiting causes loss of chloride ions, leading to high levels of aldosterone, which inhibits potassium reabsorption from the kidney tubules.