Symptoms and signs

• Often none, or neuromuscular symptoms (e.g. muscle weakness, absent reflexes, ileus), brady-tachyarrhythmia 

Investigations

Immediate

• ECG changes ‒ depressed ST, flat T, U waves, arrhythmias (arrhythmias may cause cardiorespiratory symptoms)

Helpful

• Take sample from arm without infusions running
• Venous HCO₃- ‒ when raised (metabolic alkalosis) indicates chronic potassium depletion; if <22 mmol/L in absence of GI loss, suspect renal tubular acidosis ‒ refer to renal team
• Urine K⁺ if cause not obvious
• Check serum magnesium (Mg²⁺) for persistent urine K⁺ loss especially patients with diarrhoea or on diuretics
• Carefully manage potassium supplementation in patients with impaired kidney function to minimise risk of hyperkalaemia 

Common Causes

• Blood taken from drip arm (artefact)
• Excessive gastrointestinal fluid loss
• Renal loss: urine K⁺ >20 mmol/L ‒ diuretics, mineralocorticoid excess (hyperaldosteronism and excess cortisol), Mg²⁺ deficiency see Hypomagnesaemia guideline, and renal tubular disease
• Intracellular shift (redistribution): insulin or bicarbonate treatment, theophylline, beta2-agonists, periodic paralysis, rapid blood cell proliferation
• Intravenous fluid therapy, with inadequate electrolyte replacement

• Manage K⁺. For guidance follow tool below
• Treat the underlying cause. If cause not obvious, refer to renal or endocrine team for further evaluation