ISSN 2398-2969      



Jana Gordon

Daniel H Lewis


  • Definition: serum ionized magnesium <0.35 mmol/l.
  • Magnesium is primarily an intracellular cation, with only 1% being found in the serum.
  • Extracellular magnesium exists in three forms - protein-bound, complexed with anions (such as phosphate) and ionized.
  • Ionized magnesium is the physiologically active form.
  • Total serum levels therefore may not reflect either the active moiety or the total body concentration. Intracellular magnesium is primarily in the bone (67%), muscle (2%) and other soft tissues (11%).
  • Magnesium is involved in many intra-cellular enzymatic reactions.



  • Decreased intake due to anorexia.
  • Gastrointestinal loss from profuse diarrhea, malabsorption, maldigestion.
  • Urinary loss due to renal tubular acidosis, primary renal disease, diabetes mellitus Diabetes mellitus /diabetic ketoacidosis Diabetic ketoacidosis , hyperthyroidism, hypokalemia, hypocalcemia, hypophosphatemia Hypophosphatemia.
  • Iatrogenic due to parathyroidectomy, drug administration (insulin, loop diuretics, cisplatin, aminoglycosides) or inadequate supply in intravenous fluids.

Predisposing factors

  • Magnesium is absorbed into the body from the jejunum, ileum and colon. Prolonged malnutrition or significant intestinal disease may lead to hypomagnesemia.
  • Renal homeostasis is vital for regulation of magnesium levels therefore any condition causing excessive renal loss can also result in hypomagnesemia.


  • Magnesium levels in dog and cat milk are relatively constant after the first few days of lactation. However, hypomagnesemia has been reported in around 44% of dogs with post-parturient hypocalcemia.


  • Magnesium homeostasis is mainly determind 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.
  • Magnesium deficit is most commonly associated with conditions leading to increased glomerular filtration rate or other reasons for decreased renal function.
  • A significant role for intracellular magnesium is as a co-factor for the calcium-ATP pump that moves intracellular calcium into the sacroplasmic reticulum. It performs a similar role with the sodium-potassium-ATP pump that moves these electrolytes across cell membranes. Reduction of the activity of these ion pumps is likely to be the major cause of the clinical signs of hypomagnesemia.


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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 625638. 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.

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