Hypokalaemia

🧭 When to suspect

Hypokalaemia is a serum potassium < 3.5 mmol/L and is the most common electrolyte abnormality in clinical practice. It is frequently asymptomatic and picked up incidentally on a U&E, but can cause:

• Muscle weakness, cramps, fatigue and constipation

• Most importantly, cardiac arrhythmias

In primary care the two dominant causes are:

• Non-potassium-sparing diuretics: loop diuretics such as furosemide; thiazide/thiazide-like such as bendroflumethiazide or indapamide

• Gastrointestinal losses (vomiting, diarrhoea, laxative misuse)

Other causes include:

• Transcellular shift (insulin, beta-2 agonists such as salbutamol, alkalosis, refeeding)

• Mineralocorticoid excess – primary hyperaldosteronism (Conn's syndrome) and Cushing's syndrome

• Renal tubular acidosis (RTA)

• The inherited tubulopathies (Bartter and Gitelman syndromes)

• Coexisting hypomagnesaemia, which both lowers potassium and makes it refractory to replacement

In primary care:

• Grade severity

• Decide who can be replaced safely in the community versus who needs admission

• Identify and treat the cause

• Never overlook a patient at high arrhythmia risk (on digoxin, or with heart failure, ischaemic heart disease or left ventricular hypertrophy (LVH))

Severity is clinical as well as biochemical: significant symptoms or ECG changes make any hypokalaemia an emergency, regardless of the number.

Consider an endocrine cause – particularly Conn's syndrome – in anyone with:

• Hypokalaemia and hypertension

• Recurrent unexplained hypokalaemia

Source: NHS Specialist Pharmacy Service