- Mg2+
- Red, tiger top, or gel barrier tube
- 5-7 mL of venous blood
Additional information
- 4 hrs of fasting before test
- Handle gently to prevent hemolysis
- Maintain at room temperature
- Send to lab within 45 minutes
- This test measures serum magnesium content
- Magnesium is distributed throughout the body with just 1% of body stores being present in serum and the remainder being in bone (~67%), and intracellularly (~31%)
- The kidney regulates magnesium levels through excretion or reabsorption, primarily in the distal tubule and to a lesser extent in the ascending loop of Henle
- The activity of magnesium in the body includes:
- Involved in the absorption of:
- Sodium
- Potassium
- Calcium
- Phosphorus
- Activation of many essential enzymes, as a cofactor
- Activation of enzyme systems that enable the B vitamins to function
- Essential in cellular activities:
- Calcium channel activity
- Cellular energy metabolism
- DNA, mRNA & protein synthesis
- Ion transport
- Hormone receptor binding
- Membrane stabilization
- Neurotransmission
- Regulation of blood clotting mechanisms
- Contraction of muscles
- Parathyroid hormone production (Required for production)
- Metabolism of carbohydrate, lipid, and protein
- Reactions requiring ATP as a source of energy
- Magnesium is the 4th most common cation in the body after Na, K, Ca
Magnesium is involved in many critical body processes.
Low magnesium (Hypomagnesemia):
Clinical Findings [Most pronounced when <1 mg/dL (0.41 mmol/L)]:
- Cardiac arrhythmias (atrial or ventricular)
- CNS disturbances (ataxia, nystagmus, vertigo, seizures)
- Dysarthria
- Dysphagia (Esophageal dysmotility)
- Hyperactive deep tendon reflexes
- Mental status changes (irritability, combativeness, disorientation, psychosis)
- Muscle cramping
- Neuromuscular irritability
- Tetany
- Trousseau/Chvostek signs
At risk individuals (hypomagnesemia):
- Alcoholics
- Diabetics
- Hospitalized patients
- Neonates (may see apnea, neuromuscular agitation, seizures, weakness in this group)
EKG findings (hypomagnesemia):
- ST segment depression
- T waves may be tall and peaked or may be flat or depressed in the precordium
- U waves
- Widened QRS may be present
- Decreased volatage
- PR may be prolonged
High magnesium (Hypermagnesemia):
Clinical findings
- 3-10 mg/dL (2.1-4.1 mmol/L)
- CNS depression/fatigue
- Hypotension
- Lightheadedness
- Nausea/Vomiting
- Reflexes depressed
- Skin flushing
- Vasodilation
- Weakness
- >10 mg/dL (>4.1)
- 3rd degree AV block
- Asystole (Cardiac arrest)
- Coagulation abnormalities (thrombin formation abnormalities, platelet clumping)
- CNS depression/coma/stupor
- EKG abnormalities
- Respiratory musculature paralysis
- Clinical utility of serum magnesium testing includes:
- Evaluation of:
- Electrolyte balance
- Renal disorders
- Cardiac arrhythmias
- Diabetes (Poorly controlled)
- Gastrointestinal disorders
- Neuromuscular function
- Monitoring the therapeutic efficacy of various drugs on magnesium levels
- Serum magnesium levels may remain normal even when total body stores are depleted by up to 20%
- In magnesium deficiency states, urinary magnesium decreases before the serum magnesium
- Magnesium deficiency results in the drift of calcium out of the bones, resulting in abnormal calcification in the aorta and the kidney
Additional information
- Magnesium levels are highest in winter and lowest in summer
- In women, magnesium levels decrease during menstruation
- There is an inverse relation with blood glucose levels
- Day to day variation is about 3-5%
- Three-fourths of the magnesium in the blood is found inside the red cells
- Interfering factors
- Increases by 4% in upright position
- Hemolysis leads to release of magnesium from RBCs (false hypermagnesemia)
- Venous stasis due to tourniquet use (false hypermagnesemia)
- Hyperbilirubinemia may cause false hypomagnesemia
- Related laboratory tests include:
- Aspartate aminotransferase
- Calcium
- C-reactive protein
- Creatine kinase and isoenzymes
- Homocysteine
- Kidney stone analysis
- Lactate dehydrogenase and isoenzymes
- Myoglobin
- Potassium
- Urine magnesium
- Vitamin D
Consult your laboratory for their normal ranges as these may vary somewhat from the ones listed below.
| Conv. Units (mg/dL) | SI Units (mmol/L) | |
|---|---|---|
| Adults | 1.5-2.6 | 0.62-1.07 |
| Children | 1.7-2.3 | 0.70-0.95 |
| Newborns | 1.5-2.8 | 0.62-1.15 |
| Critical low | <1.2 | <0.49 |
| Critical high | >10 | >4.1 |
Conditions associated with elevated magnesium levels (hypermagnesemia) include:
- Renal failure:
- Acute
- Chronic
- Dehydration
- Addison's disease (Adrenocortical insufficiency)
- Diabetic ketoacidosis
- Hypocalciuric hypercalcemia
- Hypokalemic metabolic alkalosis with hypomagnesuria Hypothyroidism
- Hyperparathyroidism
- Milk-alkali syndrome
- Mothers, and their infants, treated with Mg++ for eclampsia
- Multiple myeloma
- Oliguria
- Rhabdomyolysis
- Systemic lupus erythematosus
- Tissue trauma
- Tumor lysis
Drug associated with hypermagnesemia:
- Alkaline antacids
- Amiloride
- Aspirin
- Calcitriol
- Cefotaxime
- Felodipine
- Hydroflumethiazide
- Laxatives
- Lithium intoxication
- Magnesium salts
- Medroxyprogesterone
- Progesterone
- Salicylate
- Sodium bicarbonate
- Tacrolimus
- Triamterene
Conditions associated with decreased magnesium levels (hypomagnesemia) include:
- Excessive urinary losses
- Diabetic ketoacidosis (most common cause)
- Alcoholism (Osmotic diuresis)
- Acidemia
- Diabetes, poorly controlled
- Eclampsia or preeclampsia
- Glomerulonephritis (Chronic)
- Hemodialysis
- Hyperaldosteronism
- Hypercalcemic states
- Malignancy
- Hyperparathyroidism
- Vitamin D excess
- Hyperglycemia
- Hyperthyroidism
- Hypoparathyroidism
- Hypophosphatemia
- Hypokalemia
- Interstitial nephritis
- Pancreatitis (Chronic)
- Primary tubular wasting
- Hypercalciuria
- Nephrocalcinosis
- Tubular acidification defect
- Gitelman's syndrome
- Postobstructive nephropathy
- Renal failure (Acute) in diuresis phase
- Renal failure (Chronic) with magnesium wasting
- Renal tubular acidosis
- Renal transplant
- Syndrome of inappropriate secretion of antidiuretic hormone (SIADH)
- Intestinal losses or decreased absorption
- Celiac sprue
- Diarrhea (especially chronic or severe)
- Fistulas (Intestinal or biliary)
- Laxative abuse
- Malabsorption (Ileum)
- Malnutrition
- Pancreatitis
- Nasogastric suctioning (Prolonged)
- Radiation injury to bowel
- Small bowel bypass or resection
- Steatorrhea
- Alterations in distribution
- Excessive administration of glucose, insulin, or aminoacids
- Alkalemia
- Cardiopulmonary bypass surgery
- Hungry bone syndrome
- Multiple transfusions or exchange transfusions with citrated blood
- Hemodialysis
- Lactation (excessive amounts)
- Pregnancy (More common in pre-term labor)
- Sepsis syndrome
- Thermal injury
- Sweating (Excessive)
- Decreased intake
- Chronic ethanol abuse with poor diet
- Diabetics not on magnesium supplements commonly have dietary deficiency
- Diet lacking sources of magnesium (cereals, green vegetables, fruits, fish, meat)
- Prolonged intravenous therapy
- Protein-calorie malnutrition
- Starvation
- Drug induced
- Albuterol
- Aldesleukin
- Aminoglycosides antibiotics
- Amphotericin B
- Arsenic trioxide
- Azathioprine
- Basiliximab
- Bendroflumethiazide
- Bumetanide
- Calcitriol
- Calcium compounds (especially IV)
- Catecholamines
- Carbenicillin
- Cefotaxime
- Chlorthalidone
- Cisplatin
- Citrate
- Cyclosporine
- Digoxin
- Diuretics (Thiazide and Loop)
- Doxorubicin
- Ethacrynic acid
- Ethanol
- Foscarnet
- Fluoride poisoning
- Glucagon
- Haloperidol
- Hydroflumethiazide
- Insulin
- Mannitol
- Methotrexate
- Neomycin
- Oral contraceptives
- Pamidronate
- Pentamidine
- Prednisolone
- Sirolimus
- Tacrolimus
- Terbutaline
- Theophylline
- Trastuzumab
- Zalcitabine
- Atsmon J et al. Drug-induced hypomagnesaemia: scope and management. Drug Saf. 2005;28(9):763-88.
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- Nair RR et al. Alteration of myocardial mechanics in marginal magnesium deficiency. Magnes Res. 2002 Dec;15(3-4):287-306.
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- Wojcik J et al. Antepartum/postpartum depressive symptoms and serum zinc and magnesium levels. Pharmacol Rep. 2006 Jul-Aug;58(4):571-6.