Felis ISSN 2398-2950

Hypomagnesemia

Contributor(s): Jana Gordon, Daniel H Lewis

Introduction

  • 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.

Pathogenesis

Etiology

  • 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 Hyperthyroidism, hypokalemia, hypocalcemia, hypophosphatemia Hypophosphatemia.
  • Iatrogenic due to parathyroidectomy, drug administration (insulin, loop diuretics, cisplatin, aminoglycosides) or inadequate supply in intravenous fluids.

Predisposing factors

General

  • 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.  

Specific

  • 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.

Pathophysiology

  • 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.

Diagnosis

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Treatment

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Further Reading

Publications

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 (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.


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