Serum Magnesium

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Latest Edit: Iva Lloyd, ND 2021-08-24 (EDT)

See Also Lab Tests

Magnesium is the second most common intracellular cation, potassium being the first. Only 1-5% is found extracellularly. Half of the body's magnesium is found in the soft tissue and muscle cells, with the remaining found in the bone. One third of dietary magnesium is absorbed and this takes place in the small intestine. Magnesium is important for many different enzymatic reactions such as carbohydrate metabolism, protein synthesis, nucleic acid synthesis, muscular contraction, oxidative phosphorylation, ATP production, and is used by the body in the blood clotting mechanism.[1],[2]

There are three forms of serum magnesium in the plasma:

  • 1. 50% of the magneisum in the plasma is in the free/ionized form and is freely diffucible through the cell membrane
  • 2. 35% of magnesium in the plasma is protein bound
  • 3. 15% of the magnesium in the plasma is freely diffusible through the cell membrane and is complexed to other substances such as phosphate or citrate


  • serum magnesium is found intracellularly, and is therefore not the best method for assessing magnesium
  • RED blood cell magnesium is recommended for a more accurate assessment of magnesium

Patient Preparation

  • No special diet or fasting is required
  • Factors which can cause increased levels:
  • hemolytic problems (releases intracellular magnesium), dehydration
  • Drugs: thyroid medication, antacids, laxatives, calcium-containing medication, lithium, loop diuretics, aminoglycoside, aspirin use (prolonged)
  • Factors which can cause decreased levels:
  • Calcium gluconate use (within 24 hours of testing), hemodilution
  • Drugs: diuretics, some antibiotics, and insulin

Clinical Implications

Ranges: The following are the reference ranges for this lab. However, lab ranges can vary by laboratory and country. [2]

Standard U.S. Units Standard International Units
Conventional Laboratory Range 1.5-2.3 mg/dL 0.62-0.95 mmol/L
Optimal Range > 2.0 mg/dL > 0.82 mmol/L
Alarm Ranges < 1.2 mg/dL < 0.49 mmol/L

High levels indicate:

Low levels indicate:

Associated Tests


  1. Pagana Kathleen D, Pagana Timothy J, (1998) Mosby's Manual of Diagnostic and Laboratory Tests, Mosby, Inc
  2. 2.0 2.1 Weatherby Dicken, Ferguson Scott (2002) Blood Chemistry and CBC Analysis: Clinical Laboratory Testing from a Functional Perspective, Bear Mountain