Magnesium, RBC Test
An RBC magnesium test measures magnesium held inside red blood cells. Clinicians sometimes look at it to help evaluate magnesium status, since the mineral stored within cells offers a different view than magnesium measured in serum.
About this test
Magnesium is a mineral the body uses in many everyday processes, including how muscles and nerves function and how energy is handled inside cells. A red blood cell magnesium test looks at the magnesium carried inside those cells rather than the amount in the serum.
The test is done with a routine blood draw at a patient service center. A phlebotomist collects a small sample from a vein, usually in the arm, and sends it to the laboratory.
Who might consider this test?
- Others consider it to follow a situation over time or because a clinician has suggested a closer look.
Test details
| Quest code | 623 |
|---|---|
| Methodology | Inductively Coupled Plasma/Mass Spectrometry |
| Sample type | 0.5 mL packed RBC cells collected in an EDTA (lavender-top) tube or sodium heparin (royal blue-top) tube |
| Patient preparation | Avoid vitamins and mineral herbal supplements for at least one week before your blood draw. |
| Collection | Quest patient service center |
Reference range
4.0-6.4 mg/dL
Reference ranges are general guidance. The range printed on your own laboratory report is the one that applies to your result.
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Additional details
What this test looks at
This test looks at magnesium stored inside red blood cells. Since the body keeps most of its magnesium within cells, the red-cell measurement is one way to reflect that intracellular pool. Clinicians sometimes reach for it when they want a view that complements what a serum magnesium test shows.
It also helps to remember what this test is not. It does not describe the magnesium circulating in the serum, which is a separate measurement that answers a slightly different question. The two versions can be read together, and a clinician chooses based on what they are exploring.
How it's often used alongside other markers
RBC magnesium is frequently read as part of a wider look at minerals and general nutrition. Depending on what a clinician is exploring, it may be considered alongside serum magnesium or other electrolyte and mineral markers, each describing a different piece of the body's mineral balance. Read together, these markers give a fuller sense of the picture than magnesium alone.
A clinician weighs the pattern across these results, along with diet, symptoms, and personal history, before drawing any conclusions. No single marker is meant to stand in for the whole story.
Order online and a physician order is included — no doctor's visit and no insurance needed. Your sample is collected at a Quest Diagnostics patient service center.
Laboratory results should always be interpreted by a licensed clinician who knows your health history. This page is information about a test, not medical advice.
Frequently asked questions
What does an RBC magnesium test measure?
It measures magnesium held inside red blood cells. Because most of the body's magnesium sits inside cells, this offers a view of the intracellular side of magnesium status.
How is RBC magnesium different from serum magnesium?
Serum magnesium reflects the mineral circulating in the blood, while the red blood cell version reflects magnesium inside cells. A clinician chooses between them based on the question being explored.
How is the sample collected?
Through a routine blood draw at a patient service center. A phlebotomist takes a small sample from a vein in the arm and sends it to the laboratory for analysis.
Do I need to prepare for this test?
Avoid vitamins and mineral herbal supplements for at least one week before your blood draw. This is the preparation Quest publishes for this test; if your clinician gives you different instructions, follow theirs.
Why choose the red blood cell version over serum?
Some people and clinicians prefer the red-cell measurement when they want a view of magnesium inside cells to complement a serum reading. The choice depends on what a clinician is exploring.
How much does the Magnesium RBC test cost?
The cash price at Celio Health is $39. That covers the physician's order and sample collection at a Quest patient service center — no insurance is needed and there's no separate doctor's visit to pay for.