Unit Converter
Magnesium (Mg)
(Essential Electrolyte – Key Marker in Neuromuscular Function, Arrhythmias, Metabolic Disorders & Critical Care)
Synonyms
- Magnesium
- Serum magnesium
- Mg²⁺
- Plasma magnesium
- Magnesium ion concentration
Units of Measurement
- µmol/L
- mmol/L
- mg/L
- mg/dL
- mg/100 mL
- mg%
- µg/mL
- mEq/L
Molecular Weight
Magnesium ion (Mg²⁺) = 24.305 g/mol
Key Unit Conversions
1. Mass ↔ Molar
1 mmol/L = 24.305 mg/L
1 µmol/L = 0.0243 mg/L
1 mg/L = 0.0411 mmol/L
1 mg/dL = 10 mg/L = 0.411 mmol/L
1 µg/mL = 1 mg/L
2. mEq/L
Magnesium is divalent (Mg²⁺) →
1 mmol Mg2+=2 mEq1\ \text{mmol Mg}^{2+} = 2\ \text{mEq}1 mmol Mg2+=2 mEq
mEq/L = (mmol/L × 2)
mmol/L = (mEq/L ÷ 2)
3. mg%
mg% = mg/dL
Description
Magnesium is a critical intracellular cation, second only to potassium.
Functions:
- Cofactor for >300 enzymatic reactions
- DNA/RNA synthesis
- ATP metabolism (Mg-ATP complex)
- Neuromuscular transmission
- Muscle contraction & relaxation
- Heart rhythm stabilization
- Parathyroid hormone (PTH) secretion
- Insulin signaling & glucose metabolism
Magnesium disorders are common in:
- ICU
- Alcohol use
- Malnutrition
- Diabetes
- Renal dysfunction
- Proton-pump inhibitor (PPI) use
Physiological Role
1. Neuromuscular Function
Low Mg → hyperexcitability, tetany
High Mg → neuromuscular depression
2. Cardiovascular Function
- Prevents arrhythmias
- Required for Na⁺/K⁺ ATPase function
- Critical in torsades de pointes management
3. Bone Metabolism
~60% of Mg stored in bone
4. Hormone Regulation
- Required for PTH secretion
- Modulates insulin action
5. Electrolyte Balance
Low Mg frequently causes:
- Hypocalcemia
- Hypokalemia
Clinical Significance
HIGH Magnesium
(Usually seen in renal failure or excessive intake)
Causes
- Renal failure (most common)
- Excess Mg intake (antacids, laxatives)
- Iatrogenic MgSO₄ therapy (eclampsia, torsades)
- Adrenal insufficiency
- Tumor lysis syndrome
- Lithium therapy
Symptoms
- Nausea, flushing
- Hypotension
- Muscle weakness
- Diminished deep tendon reflexes
- Bradycardia
- Heart block
- Respiratory depression
- Cardiac arrest (Mg >6–8 mEq/L)
LOW Magnesium
(Common & clinically important)
Causes
- Alcohol abuse
- Chronic diarrhea
- Malnutrition
- PPI use
- Uncontrolled diabetes
- Diuretics (loop, thiazide)
- Aminoglycosides, amphotericin
- Cisplatin therapy
- Refeeding syndrome
- Hyperaldosteronism
Symptoms
- Paresthesia
- Tremors
- Muscle cramps
- Seizures
- Torsades de pointes
- Ventricular arrhythmias
- Hypocalcemia
- Hypokalemia
Reference Intervals
(Tietz 8E + Mayo + ARUP + nephrology standards)
Serum Magnesium
- 0.75 – 0.95 mmol/L
(= 1.8 – 2.3 mg/dL)
(= 1.5 – 1.9 mEq/L)
Mild Hypomagnesemia
- 0.60 – 0.75 mmol/L (1.5 – 1.8 mg/dL)
Severe Hypomagnesemia
- <0.50 mmol/L (<1.2 mg/dL)
Hypermagnesemia
- >1.05 mmol/L (>2.6 mg/dL)
Critical Levels
- >1.5 mmol/L → risk of paralysis, respiratory depression
- >2.0 mmol/L → cardiac arrest
Diagnostic Uses
1. Electrolyte Evaluation
Workup of:
- Hypocalcemia
- Hypokalemia
- Refractory hypokalemia (Mg deficiency prevents K⁺ repletion)
2. Arrhythmia Management
Mg is critical in:
- Torsades de pointes
- Digoxin toxicity
- Ventricular arrhythmias
3. Neuromuscular Symptoms
Evaluate cramps, spasms, tremors, seizures.
4. Diabetic Patients
Mg depletion common in uncontrolled glycosuria.
5. ICU/Critical Care
Used to guide replacement therapy.
6. Obstetrics
Monitor Mg levels during MgSO₄ therapy for:
- Severe preeclampsia
- Eclampsia
- Preterm labor neuroprotection
7. Renal Disease
Mg accumulates due to reduced filtration.
Analytical Notes
- Serum magnesium reflects 1% of total body Mg (limitations)
- Better marker: ionized magnesium (not widely available)
- Avoid hemolysis (RBCs high in Mg)
- Non-fasting sample acceptable
- Interpret with Ca²⁺ and K⁺ levels
- PPIs cause chronic Mg loss
Clinical Pearls
- Hypomagnesemia is the mother of hypokalemia - you cannot correct K⁺ without Mg.
- Low Mg suppresses PTH → hypocalcemia.
- MgSO₄ is life-saving in eclampsia and torsades.
- Alcoholics commonly have profound Mg deficiency.
- Hypermagnesemia is almost always due to renal failure or excessive supplementation.
Interesting Fact
Magnesium is involved in all ATP-dependent reactions in the body - meaning life literally runs on Mg-ATP, not ATP alone.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Electrolytes
- Endocrine Society / AACE - Electrolyte Management Guidelines
- Mayo Clinic Laboratories - Magnesium
- ARUP Consult - Electrolyte Disorders
- MedlinePlus / NIH - Magnesium Test