What is this test?
Magnesium supports nerves, muscles, heart rhythm and many enzymes. Blood magnesium is useful for significant deficiency or excess but represents only a small part of total body stores.
Why might it be ordered?
- To investigate weakness, cramps, arrhythmia or an electrolyte disturbance.
- To monitor kidney disease, gastrointestinal loss or medicines that alter magnesium.
What sample is needed?
A blood sample is required. The laboratory chooses the correct tube and handles the sample for this test.
How should you prepare?
Ask the laboratory whether you need to fast or attend at a particular time. Do not stop or change medicines or supplements unless your clinician tells you to.
How should you understand the result?
A normal serum value does not exclude every mild tissue deficiency. Kidney function and calcium and potassium results help with interpretation.
Sources and editorial status
This patient-facing text is an editorial draft. It should be approved by a laboratory physician before official publication.