Minerals & trace elements
Magnesium (serum)Mg
Cofactor for >300 enzymes; serum reflects only ~1% of body stores.
Sample
Serum
Clinical reference range
1.7 to 2.4 mg/dL
Adult
Conv: 1.7–2.4 mg/dLFunc: 2–2.4 mg/dL
Biology
What it measures
60% in bone, 39% intracellular, 1% extracellular. Renal regulation through TRPM6/7 in distal nephron.
Clinical use
Why we order it
Investigate refractory hypokalemia/hypocalcemia, arrhythmia, alcoholism, PPI use.
Lens · Clinical
Interpretation by lens
Clinical interpretation
Empirically replete in any unexplained refractory hypokalemia or torsades de pointes.
Differential
Causes of abnormal values
Causes of LOW
- ↓Diuretics, PPIs, aminoglycosides, cisplatin
- ↓Alcoholism
- ↓Refeeding syndrome
- ↓Diarrhea, malabsorption
Pitfalls
Pre-analytic & interpretation traps
- !Serum Mg can be normal despite severe intracellular depletion. RBC Mg or magnesium loading test is more accurate but rarely available.
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