Canis ISSN: 2398-2942


Contributor(s): Jana Gordon, Daniel H Lewis


  • Definition: serum ionized magnesium >0.55 mmol/l.
  • Magnesium is primarily an intracellular cation, with only 1% being found in the serum.
  • Extracellular magnesium exists in three forms - ionized (55%), protein-bound (20-30%), and complexed forms (15-25%).
  • Ionized magnesium is the physiologically active form.
  • Total serum levels may not reflect either the active moiety or the total body concentration.
  • Intracellular magnesium is primarily in the bone (67%), muscle (20%) and other soft tissues (11%).
  • Magnesium is involved in many intra-cellular enzymatic reactions.



  • Magnesium homeostasis is mainly determined by renal elimination and reabsorption. 80% of total serum magnesium is filtered by the glomerulus. 10-15% is reabsorbed in the proximal tubule, 60-70% in the cortical thick ascending loop of Henle, 10-15% in the distal convoluted tubule.
  • Gastrointestinal absorption of magnesium occurs mainly in the ileum, although the jejunum and colon also contribute. The control of magnesium absorption from the GI tract has not yet been fully elucidated.
  • Magnesium accumulation is most commonly associated with conditions leading to decreased glomerular filtration rate or other reasons for decreased renal function.
  • Iatrogenic hypermagnesemia due to excessive intravenous or oral administration (not reported in small animals but seen in people).
  • Magnesium concentrations are much higher within erythrocytes than in serum; marked hemolysis may result in mild hypermagnesemia.

Predisposing factors


  • Conditions causing decreased glomerular filtration may lead to hypermagnesemia.



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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Martin L G, Matteson V L, Wingfield W E et al (1994) Abnormalities of Serum Magnesium in Critically Ill Dogs: Incidence and Implications. J Vet Emerg Crit Care 4 (1), 15-20 VetMedResource.

Other sources of information

  • Marino P (2007) Renal and Electrolyte Disorders: Magnesium. In: The ICU Book. pp 625-638. Lippincott, Williams & Wilkins.
  • Bateman S (2006) Disorders of Magnesium: Magnesium deficit and excess. In: Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice. pp 210-226. Ed. S. DiBartola, Saunders Elsevier.