Magnesium (Mg²⁺)

The underappreciated electrolyte — critical for hundreds of enzymatic reactions.

What it is

Magnesium is involved in over 300 enzymatic reactions in the body, including ATP production, protein synthesis, DNA repair, and nerve conduction. The vast majority is stored intracellularly and in bone, making blood levels an imperfect reflection of total stores.

Why it matters

Cisplatin-based chemotherapy causes significant magnesium wasting by the kidneys. Chronic hypomagnesaemia causes muscle cramps, fatigue, potassium wasting (making it hard to correct potassium without first addressing magnesium), and cardiac arrhythmias. It is frequently underdiagnosed.

How to test

Standard electrolyte or renal panel. RBC magnesium is a better indicator of intracellular stores but less commonly ordered.

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

Optimal range

Below 0.75 mmol/L

hypomagnesaemia — supplement and investigate

0.75–0.95 mmol/L

normal

How often

Each oncology blood panel. More frequent if on platinum-based chemotherapy.