The Best and Worst Methods of Testing Magnesium Levels

We know that 99% of our total body magnesium is intracellular, which makes testing for deficiency difficult using standard methods. A review of the literature on magnesium deficiency outlines the most reliable methods of testing magnesium levels in the human body.

More Reliable Methods of Testing

  • Retention of magnesium load after intravenous administration is likely the best indicator of magnesium deficiency.  This assumes normal kidney function for intravenous magnesium.
  • Retention of magnesium load after oral after its administration.  Assumes normal kidney function normal gastrointestinal and renal function.
  • Mononuclear cell magnesium
  • Muscle magnesium content (muscle biopsy)

Less Reliable Methods of Testing

  • Hair magnesium content
  • Bone magnesium
  • Ratio of ionized magnesium to total magnesium (serum or plasma)
  • Ionized magnesium levels – controversial and not always available in clinical labs and hard to measure reliably
  • Lymphocyte magnesium
  • Urinary or faecal magnesium excretion (low or high levels may indicate deficiency)
  • Urinary fractional magnesium excretion >4% (some authors have suggested >2% in those with normal kidney function)
  • Total erythrocyte magnesium levels (magnesium deficiency has been suggested when erythrocyte magnesium levels are <1.65 mmol/L)
  • Total serum magnesium levels
    • Normal serum magnesium is considered to be 0.7–1 mmol/L
    • Optimal serum magnesium concentration is proposed at >0.80 mmol/L
    • A serum magnesium <0.82 mmol/L (2.0 mg/dL) with a 24-hour urinary magnesium excretion of 40–80 mg/day is highly suggestive of magnesium deficiency
    • Magnesium supplementation is recommended in subjects experiencing symptoms that reflect magnesium deficiency if the serum level is below 0.9 mmol/L
    • When serum levels are less than 0.8 mmol/L, magnesium supplementation is necessary

“It is important to note that choosing only one of the aforementioned methods of measuring magnesium deficiency is not appropriate for diagnosing magnesium deficiency. In general, either symptoms of magnesium deficiency must accompany the more reliable methods to diagnose magnesium deficiency (eg, intravenous/oral magnesium load, mononuclear cell or muscle), or two or more of the reliable measurements (eg, intravenous/oral magnesium load, mononuclear cell or muscle) should be used in supporting a diagnosis of magnesium deficiency”


  1. DiNicolantonio, j et al. Subclinical magnesium deficiency: a principal driver of cardiovascular disease and a public health crisis. Open Heart. Jan 13, 2018. Accessed at:
Share on facebook
Share on twitter
Share on linkedin
Share on pinterest
Share on facebook
Share on facebook
Share on twitter
Share on linkedin
Share on email
Get the best of the
Stay Calm blog sent to your inbox