Empeiria

Magnesium

Also known as Mg, serum magnesium

Mg²⁺ inorganic ion

LOINC 19123-9 code verified serum mg/dL

What this substance is

formula
Mg²⁺
mass
24.305 g/mol
monoisotopic
23.98394
charge
2
nucleus
12 protons, 12 neutrons (24Mg)
electrons
10: 1s² 2s² 2p⁶
InChIKey
JLVVSXFLKOJNIY-UHFFFAOYSA-N
ChEBI
CHEBI:18420

Drawn from ChEBI's own curated 2D drawing, accepted only after its InChIKey, formula and charge matched the ChEBI release. Nothing here is hand-entered. Two masses are given because they answer different questions: the average is natural-abundance weighted and drives unit conversion; the monoisotopic value uses only the commonest isotope of each element and is what mass spectrometry measures.

3D model · Magnesium

A schematic atom: a nucleus of 12 protons and 12 neutrons (the most common isotope, 24Mg), inside its electron shells, 1s² 2s² 2p⁶. The configuration matches the NIST Atomic Spectra Database ground state of Mg III (1S0). The cloud is drawn as nested spheres because that term is an S state: the electron density really is spherical. Not to scale: shells are spaced on a square-root scale so the inner ones stay visible, and the nucleus is magnified about ten-thousand-fold.

Reference ranges

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This open edition shows a range only where a public-domain or openly licensed source states one, and none does for this marker yet. Compare your result with the range printed on your own lab report.

How it is measured

In practice

A health worker takes a small blood sample from a vein in your arm. There is usually nothing to do to get ready. If other blood tests are done at the same time, you may need to skip food and drink for a few hours. Blood levels can look normal even when the body's stores are low.

Serum magnesium is measured on a venous blood sample, usually without preparation; fasting may apply if other tests are drawn at the same time, and medicines and supplements should be disclosed. Because bone stores buffer the serum level, a urine magnesium or red blood cell magnesium test may be added; the RBC test may detect deficiency better.

Before the test

  • Tell your provider about all prescription and over-the-counter medicines and supplements you take.

Where: laboratory

Source: Magnesium Blood Test -- MedlinePlus Medical Tests, U.S. National Library of Medicine cited · not yet checked by a person

In the lab

enzymatic colorimetric

Xylidyl blue / calmagite

A dye binds magnesium and changes colour in proportion to it.

In alkaline solution magnesium forms a purple complex with xylidyl blue, with EGTA added to mask calcium; the fall in dye absorbance at 600 nm is read photometrically.

Why labs disagree: Only about 1% of body magnesium is outside cells and about 0.3% is in serum; most is in bone and inside cells. Serum magnesium therefore does not reflect total body magnesium, and a normal result does not exclude depletion.

Sources: Jahnen-Dechent W, Ketteler M. Magnesium basics. Clin Kidney J 2012 (PMC open access); Laboratory Procedure Manual, Magnesium (Roche cobas), NHANES August 2021 - August 2023, CDC/NCHS cited · not yet checked by a person

What it reports on

Associated symptoms

Conditions this marker features in

When low
  • low Low blood magnesium · defining
    Typically defined as serum magnesium below 0.66 mmol/L (1.6 mg/dL). Serum holds under 1% of body magnesium, so a normal result does not rule out low body stores.
  • low Low blood calcium · supportive
    Part of the first work-up. Low magnesium is a cause, for example with acid-reducing PPI medicines, and must be treated as well.
  • low Low blood potassium · supportive
    Low magnesium comes with more than half of significant cases, and must be corrected for potassium treatment to work.

Ordered as part of

renal · vitamins