EBM Consult

Lab Test: Magnesium (Blood) Level

    Lab Test
    • Magnesium (Blood)
    • Used to identify magnesium deficiency or overload.  Magnesium is a cofactor used by more than 300 different enzymes and reactions in the body.  These include:
      • Energy production, oxidative phosphorylation, & glycolysis
      • DNA and RNA synthesis
      • Protein synthesis
      • Active transport of calcium and magnesium across cell membranes
      • Muscle and nerve function
      • Structural development of bone
      • Glucose control
      • Regulation of blood pressure and cardiac rhythms
    Reference Range
    • Adult: 
      • 1.5 - 2.3 mg/dL
      • SI (1.3 - 2.1 mEq/L;  0.65-1.05 mmol/L)
    • Child:  1.4 - 1.7 mEq/L
    • Newborn:  1.4 - 2 mEq/L
    • Critical Values:
      • < 1.2 mg/dL  or > 4.9 mg/dL
      • < 1 or > 9 mEq/L
    Indications & Uses
    • Alcohol abuse (chronic)
    • Cardiovascular Disease due to increases in cardiac irritability and risk of cardiac dysrhythymias in patients with low Mg
    • Chronic kidney disease
    • Hyperaldosteronism
    • Hyperthyroidism
    • Hypoparathyroidism
    • Ingestion of magnesium-containing antacids
    • Malnutrition or malabsorption syndromes including postoperative patients who may not eat for 5 to 7 days and whose metabolism is accelerated with refeeding. 
    • Pre-eclampsia or eclampsia (of pregnancy) receiving magnesium infusions
    Clinical Application
    • For increased Mg levels:
      • Addison disease:  Aldosterone enhances magnesium excretion.  With reduced aldosterone, magnesium excretion is diminished.
      • Renal insufficiency:  Magnesium is excreted by the kidneys.  With end-stage renal failure, excretion is reduced and magnesium accumulates in the blood. 
      • Ingestion of magnesium-containing antacids or salts.
      • Hypothyroidism:  The pathophysiology is unknown. 


    • For decreased Mg levels:
      • Alcoholism:  Ethanol increases the renal elimination of magnesium in the urine.
      • Diabetic ketoacidosis (DKA):  The use of insulin is known to cause glucose movement into the cells along with magnesium.
      • Malnutrition resulting in poor intake.
      • Malabsorption:  The major source of magnesium is dietary intake and absorption from the intestines and either situation can cause hypomagnesemia.  Furthermore, patient with malabsorption will also have fat-soluble vitamins loss, including vitamin D levels which cause hypocalcemia and eventually hypomagnesemia. 
      • Hyperparathyroidism:  In this disease, calcium levels are reduced.  Calcium enhances intestinal absorption of magnesium, and with low calcium levels, magnesium is not well absorbed.  In hyperparathyroidism, calcium levels are high and magnesium levels increase. Renal tubular disease (chronic):  Magnesium is reabsorbed in the renal tubule.  Diseases affecting this area of the kidney (e.g., tubular necrosis) or drugs that are toxic to the renal tubule (e.g., aminoglycosides) will allow increased losses of magnesium in the urine.
    Related Tests
    • Potassium (Serum)
    • Sodium (Serum)
    Drug-Lab Interactions
    • Hemolysis of the collected blood sample can create falsely elevated levels of magnesium. 
    • Drugs that increase magnesium levels include antacids, aminoglycoside, calcium-containing medications, laxatives, lithium, loop diuretics, and levothyroxine.
    • Drugs that decrease magnesium levels include some foscarnet, loop diuretics, and insulin.
    Test Tube Needed
    • Red or green top tube.
    What To Tell Patient Before & After
    • Explain procedure to the patient.
    • Tell the patient that no special diet or fasting is required.
    • Quamme GA et al. Clin Lab Med 1993;13(1):209-33.
    • Hujgen J et al. Am J Clin Pathol 2000;114(5):688-95.
    • Pagana K, Pagana TJ eds. Mosby's Manual of Diagnostic and Laboratory Tests. 5th Ed.  St. Louis, Missouri. 2014.

MESH Terms & Keywords

  • Magnesium, Mg, Mg Lab, Mag Level, Mag Lab Test