Blood biochemistry: magnesium

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Sections available in full article Overview, Uses, Sampling, Source of test material, Quantity of test material, Sample collection technique, Quality control, Test (s), Methodologies, Availability, Technique (intrinsic) limitations, Result data, Normal (reference) values, Abnormal values, Sources, Publications, Vetstream contributor(s),
Contributors Dr Kathleen P Freeman DVM MS PhD MRCVS
Ms Yvonne McGrotty BVMS CertSAM DipECVIM-CA MRCVS European Specialist in Internal Medicine

Overview

  • Magnesium (Mg) is the second most abundant intracellular cation (after potassium).
  • Magnesium is a cofactor for the sodium potassium ATPase pump and maintains electrical excitability in muscles and nerves.
  • Most of the total Mg stores are found within bone (around 60%) with the remainder located intracellularly in soft tissue.
  • Plasma/serum Mg may represent <1% of total body magnesium and therefore serum levels may not accurately reflect total body stores.
  • Approximately 30% of serum Mg is bound to proteins (albumin and globulin).
  • Ionized Mg (iMg2+) is the biologically active fraction that is essential for regulating intracellular homeostasis.
  • Intracellular magnesium is involved with calcium and potassium balance.
  • Magnesium balance is controlled by gastrointestinal tract absorption (mainly in jejunum and ileum) and by renal excretion.
  • Magnesium imbalance appears to be a common occurrence in critically ill animals.
  • Decreased magnesium can result in refractory hypokalemia Hypokalemia due to intracellular potassium loss.
  • Hypomagnesemia Hypomagnesemia may cause hypocalcemia Hypocalcemia through reduced parathyroid hormone secretion and can lead to seizures.
  • Decreased magnesium can lead to hyperexcitability, collapse and seizures.

Uses

In combination

  • Other blood biochemistry and laboratory findings.

Result data

Normal (reference) values

  • Check with laboratory for reference values established for its method/equipment and population used.
  • Example of reference values in small animals: 0.7-1.2 mmol/l (1.8-3.0mg/dl).

Abnormal values

Increase (rare)

  • Decreased urinary excretion (renal failure).
  • Hemolysis.
  • Iatrogenic.
  • Hyperparathyroidism Hyperparathyroidism (primary).
  • Hypoadrenocorticism Hypoadrenocorticism.

Decrease

  • Intestinal losses (eg diarrhea, malabsorption).
  • Anorexia.
  • Renal losses.
  • Administration of fluids deplete in magnesium (eg Lactated Ringers Solution, 0.9% sodium chloride).
  • Endocrine disease (eg diabetes mellitus Diabetes mellitus /diabetic ketoacidosis Diabetic ketoacidosis , hypoparathyroidism Primary hypoparathyroidism ).
  • Glycosuria.
  • Hypoproteinemia Hypoproteinemia.

Clinical manifestations

  • Hypermagnesemia Hypermagnesemia :
    • Clinical signs not usually apparent unless severe elevation present.
    • Prolongation of PR interval and widening of QRS complex.
    • Muscle paralysis.
  • Hypomagnesemia Hypomagnesemia :
    • Cardiac arrhythmias.
    • Muscle weakness, fasiculations, ataxia or seizures (more likely when concurrent hypokalemia or hypocalcemia present).
    • Refractory hypokalemia.
  • Treatment of hypomagnesemia:
    • Treat underlying cause.
    • IV supplementation if rapid repletion necessary (dilute in 5% dextrose).
    • Chronic hypomagnesemia can be treated with oral supplementation.

Sources

Publications

Refereed papers

  • Recent references from PubMed.

Other sources of information

  • Mathews K (2006) Magnesium. In: Veterinary Emergency and Critical Care Manual.2nd edition. Eds Mathews, K. Lifelearn Inc., Ontario pp 403-405.
  • Hansen B (2000) Disorders of Magnesium. In: Fluid Therapy in Small Animal Practice.2nd edition. Eds DiBartola, S.P. WB Saunders, Philadelphia pp175-186.

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