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Marker · Educational ranges, not diagnosis

RBC magnesium

Also called red-cell magnesium, erythrocyte magnesium.

Magnesium measured inside red cells rather than in serum. Serum holds about 0.3 percent of body magnesium, which is why a normal serum value can sit next to depleted tissue stores.

Read this first

  • Coach, not doctor. Aaron Cuha is a coach, not a doctor. No clinical credential is claimed for him, or for these pages. A number on a panel is a conversation starter with a clinician, not a DIY diagnosis. Nothing here is a prescription, a protocol, or a reason to start or stop a medicine. Educational use only. This database summarizes published research and is not medical advice. Where a dose appears it is a record of what a trial or clinic ran, or what people describe doing, with its source attached. Nothing here is a recommendation for personal use.
  • Affiliate disclosure. Knowledge stays free. Every page, every guide and every tool is free to read and stays free. Lab-panel affiliate links, when they exist, live on /bloodwork/partners and print what is earned on the row, or that nothing is earned today. This glossary does not sell panels. The Archive does not order labs.
  • Three lab stories stay separate. /bloodwork is the human panel. /testing and /prices/labs are peptide certificate chemistry. /supplements/quality is what is in the bottle.

Why a longevity audience asks

The owner's floor list uses RBC magnesium, not serum, as the conversation marker. The blood-pressure effect of supplementation is real and small. Sleep and brain claims are much thinner than the marketing.

How a coach reads it

There is no single consumer cut-off this site will print as a diagnosis. Ask the lab for its RBC method and interval. Treat serum magnesium as context, not reassurance. The owner takes magnesium glycinate on the floor list and still wants the RBC number.

Units on this page: mg/dL, mmol/L

When it is low

May mean intake is low, losses are high, or serum is being defended while tissue is not. Symptoms such as cramps do not diagnose a low RBC value, and a low value does not diagnose those symptoms.

When it is high

High magnesium, especially with reduced kidney function, is a clinician problem. Do not add more magnesium to chase a feeling if the kidneys are not cleared for it.

Easy ways to misread it

  • Serum magnesium is the test most panels run, and it is the one most likely to look fine.
  • Labels quote salt weight, not elemental magnesium.
  • Kidney disease changes the safety of the bottle. That is a clinician gate.

What to ask a clinician

Ask for RBC magnesium, not serum alone. Mention kidney disease, diuretics, or GLP-1 / low-carb eating if that is your context.

Related supplements

Related when-playbooks

Sources on this page