How to prepare
No fasting is required for this test. Drink water as normal beforehand.
If you currently take magnesium supplements, check with your practitioner whether to pause them before testing to get an accurate baseline.
This test is only available at Healius pathology centres. When booking, confirm your nearest Healius location. A healthcare professional will take a blood sample from a vein in your arm.
After the test
Share your results with your GP, integrative practitioner, or nutritionist. If your RBC magnesium is low, they may investigate contributing factors such as dietary intake, gastrointestinal absorption, medication effects, or chronic health conditions.
If you are actively managing a condition where magnesium status is relevant, such as diabetes or a heart rhythm disorder, your practitioner may use this result to guide supplementation or monitor progress over time.
Your test results will be available in your private dashboard. If there are any urgent issues, we'll let you know so you can follow up with your health professional.
Understanding results
Results are reported as magnesium concentration inside red blood cells, typically in millimoles per litre (mmol/L). Reference ranges vary between laboratories; your result report will include the applicable range.
RBC magnesium reflects tissue stores more accurately than serum magnesium because it measures what's inside cells rather than what's circulating in the plasma. A low RBC magnesium result, even with a normal serum result, may suggest that cellular magnesium stores are depleted.
Your practitioner will interpret your result alongside your symptoms, diet, medications, and other relevant investigations to determine whether a deficiency is present and what action, if any, is appropriate.
