Hypokalaemia is defined as serum potassium concentration below 3.5 mmol/l. It can be divided into:
- mild - 3.1-3.5 mmol/L
- moderate - 2.5-3.0 mmol/L
- severe - <2.5 mmol/L (1)
The condition is one of the commonest electrolyte disturbances encountered in the clinical practice
- around 3% of unselected patients is thought to be hypokalaemic on admission to the clinic, however during the hospital stay, >20% are likely to develop hypokalaemia due to iatrogenic causes e.g. - prescribed drugs etc
- one fifth of these patients will have moderate to severe hypokalaemia
- an increased risk of hypokalaemia is seen especially in
- psychiatric patients - due to the medication rather than their underlying illness
- patients on peritoneal dialysis - due to a combination of K+ loss into peritoneal fluid, infection and poor nutrition (1,2)
Women are thought to be more susceptible to hypokalaemia than men, especially when given thiazide diuretics. This is probably due to reduced muscle mass and a smaller pool of exchangeable K+ (2)
Pseudohypokalaemia related to seasonal (summer) changes in ambient temperature has been described in some literature. It is caused by metabolic increases in Na+,K+- ATPase (‘sodium pump’) activity and cellular uptake of K+ (2).
Note that hypokalaemia exacerbates digoxin toxicity.