Serum Magnesium Levels
Introduction
- Essential intracellular cation crucial for multiple physiological processes
- Second most abundant intracellular cation after potassium
- 99% of total body magnesium is intracellular
- Only 1% present in extracellular fluid and measurable in serum
Distribution in Body
- Bones: 60-65% of total body magnesium
- Soft tissues: 34-39%
- Extracellular fluid: ~1%
- Serum magnesium exists in three forms:
- Ionized (55-70%)
- Protein-bound (20-30%)
- Complexed (5-15%)
Physiological Role
Critical Functions
- Neuromuscular transmission
- Enzyme cofactor (>300 enzymatic reactions)
- Energy metabolism
- Protein synthesis
- Cardiac conduction
- Bone formation
- Cell membrane stability
Homeostatic Regulation
- Intestinal absorption (30-50% of dietary intake)
- Renal handling (primary regulation site)
- Bone exchange
- Hormonal influences:
- Parathyroid hormone
- Vitamin D
- Calcitonin
Testing Indications
Primary Indications
- Unexplained muscle weakness
- Cardiac arrhythmias
- Seizures
- Tetany
- Chronic diarrhea
- Malabsorption syndromes
- TPN monitoring
- Diabetes mellitus
High-Risk Conditions
- Chronic kidney disease
- Malnutrition
- Burns
- Chemotherapy
- Long-term diuretic use
- Inflammatory bowel disease
Interpretation Guidelines
Reference Ranges
Age-Specific Normal Values
- Preterm neonates: 1.6-2.4 mg/dL
- Term neonates: 1.5-2.2 mg/dL
- Infants: 1.6-2.2 mg/dL
- Children: 1.7-2.2 mg/dL
- Adolescents: 1.7-2.2 mg/dL
Clinical States
- Hypomagnesemia: <1.7 mg/dL
- Mild: 1.5-1.7 mg/dL
- Moderate: 1.0-1.5 mg/dL
- Severe: <1.0 mg/dL
- Hypermagnesemia: >2.2 mg/dL
- Mild: 2.2-3.0 mg/dL
- Moderate: 3.0-5.0 mg/dL
- Severe: >5.0 mg/dL
Clinical Management
Hypomagnesemia Management
- Acute Treatment:
- IV magnesium sulfate: 25-50 mg/kg/dose
- Maximum single dose: 2 grams
- Monitor cardiac rhythm during administration
- Chronic Management:
- Oral supplementation
- Dietary modification
- Treatment of underlying cause
Hypermagnesemia Management
- Discontinue magnesium-containing medications
- IV calcium gluconate for severe symptoms
- Diuresis in renal-competent patients
- Dialysis in severe cases or renal failure
Monitoring Parameters
- Serial magnesium levels
- ECG changes
- Deep tendon reflexes
- Respiratory status
- Concurrent electrolytes (especially calcium and potassium)
Further Reading
