Potassium (K⁺)

Cardiac and muscle function depend on a narrow potassium window.

What it is

Potassium is the primary intracellular cation and is critical for nerve conduction, muscle contraction, and cardiac rhythm. The extracellular concentration is tightly regulated within a narrow range.

Why it matters

Many chemotherapy drugs, diuretics, and the diarrhoea/vomiting associated with treatment deplete potassium. Hypokalaemia causes muscle weakness, cramping, and dangerously abnormal heart rhythms. It is one of the most important electrolytes to monitor during treatment.

How to test

Standard electrolyte panel.

This information is for educational purposes only. Always discuss testing and interpretation of results with your care team.

Optimal range

Below 3.5 mmol/L

hypokalaemia — risk of arrhythmia, weakness

3.5–5.0 mmol/L

normal

Above 5.0 mmol/L

hyperkalaemia — cardiac risk

How often

Before each chemotherapy cycle, and with any significant vomiting or diarrhoea.