Relationship between skeletal muscle intracellular ionized magnesium and measurements of blood magnesium.
Level 4 - case-series / case-control
Cross-sectional comparative study in healthy volunteers
PubMed 8636650 · doi:10.1016/s0022-2143(96)90080-3
What was done
In 60 healthy adult subjects, intracellular ionized magnesium in resting skeletal muscle was measured in vivo using phosphorus-31 magnetic resonance spectroscopy. Blood magnesium concentrations were simultaneously measured in serum, serum ultrafiltrate, mononuclear blood cells, and red blood cells using atomic absorption spectroscopy or a colorimetric assay.
What was found
Mean values (mean +/- SD) were: skeletal muscle intracellular ionized magnesium = 557 +/- 97 mumol/L; serum magnesium = 0.78 +/- 0.09 mmol/L; serum ultrafiltrate magnesium = 0.60 +/- 0.12 mmol/L; mononuclear blood cell magnesium = 13.8 +/- 2.3 mmol/L; and red blood cell magnesium = 1.92 +/- 0.33 mmol/L. There was a significant negative correlation between muscle intracellular ionized magnesium and serum magnesium (r = -0.43, p < 0.05). Compared with men, women had significantly lower serum magnesium (p < 0.05) and significantly higher muscle intracellular ionized magnesium (p < 0.05). Neither measure correlated with age. Correlation values for the other blood compartments were not reported in the abstract.
Why it matters
Standard clinical testing relies on serum magnesium, but these findings show that serum levels do not positively reflect biologically active intracellular ionized magnesium in skeletal muscle, the body's primary soft tissue magnesium store.
Limits
The study is cross-sectional and limited to 60 healthy adults, precluding assessment in clinical populations with suspected magnesium deficiency or overload. The abstract does not provide correlation coefficients or p-values for ultrafiltrate, red blood cell, or mononuclear blood cell measurements.
Cited by
- supports Serum magnesium testing does not accurately reflect total body magnesium status because most magnesium resides intracellularly.