Magnesium

What it measures

Magnesium is an intracellular cation needed for enzyme function, nerve conduction and heart rhythm. It is checked in arrhythmias, refractory low potassium or calcium, alcohol use and during pre-eclampsia treatment.

Specimen and preparation

• Specimen: Serum or lithium-heparin plasma
• Tube: Gold top
• Preparation: Avoid haemolysis; do not use EDTA or citrate tubes.

Reference range

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

• Kidney failure
• Magnesium sulphate therapy (pre-eclampsia)
• Excess antacid or laxative use
• Haemolysed sample

Causes of low values

• Alcohol use disorder
• Proton pump inhibitors and diuretics
• Diarrhoea and malabsorption
• Refeeding syndrome
• Poorly controlled diabetes

Method

Colorimetric (xylidyl blue or calmagite) or enzymatic

Good to know

Serum level may be normal despite total body depletion. Therapeutic range for pre-eclampsia is about 4–7 mg/dL.

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