Why Is My Dog Or Cat‘s Blood Magnesium Level Low Or High?

Ron Hines DVM PhD

See What Normal Blood & Urine Values Are

Causes Of Most Abnormal Blood & Urine Tests

See How Tests Are Grouped

Your Pet’s Blood Magnesium Level = Mg

After sodium (Na+), potassium (K+) and calcium (Ca2+), magnesium (Mg2+) is the most common positive ion (cation), in your dog or cat’s blood stream. Magnesium is required for many enzyme-based reactions that occur in your pet’s body. Within the animal’s cells, magnesium it is second only to potassium in abundance. The normal commercial diets for dogs and cats contain plenty of magnesium because meat and meat byproducts are rich magnesium sources.

Approximately fifty percent of the magnesium in your dog and cat’s body is found in its bones. Most of the other half is found inside the cells of its body. Only about 1% of your dog or cat’s magnesium is found in its blood. The pet’s body works hard to keep that amount constant. So, when your veterinarian says that your pet is deficient in magnesium based on a blood test, that doesn’t necessarily mean that all its body magnesium reserves are low.

Too little blood magnesium (hypomagnesemia) is considerably more common in dogs and cats than too much blood magnesium (hypermagnesemia).

Reasons Why Your Cat Or Dog’s Blood Magnesium Level Could Be Low (Hypomagnesemia):

Pets that are critically ill from any cause can have fluctuations in their blood mineral cations – including magnesium.

Intestinal disease that prevents proper magnesium absorption or sustained (long term) diarrhea can also lower your pet’s blood magnesium level. Magnesium can also migrate out of the blood during acute pancreatitis. Failing kidneys that compensate by producing large amounts of dilute urine can also allow too much blood magnesium to escape from your pet’s body.

Failure to eat/starvation and inappropriate or bizarre diets can cause your pet’s magnesium level to be low. So can hepatic lipidosis in cats.

Uncontrolled diabetes in cats and in dogs that causes excessive urination (polyuria) can lower blood magnesium levels. Hyperthyroidism in cats and low parathyroid gland activity (hypoparathyroidism) have also caused blood magnesium levels to be low.

Pets that receive excessive amounts of diuretics (e.g. furosemide/Lasix® often given for heart disease) can cause blood magnesium level to be low. Intravenous feeding in hospitalized pets or pets given large amounts of magnesium-free IV fluid can also experience low blood magnesium. (In humans, aminoglycosides [like gentamicin], digoxin, amphotericin B and cyclosporin have all been associated with low blood magnesium level. We veterinarians do not know if that occurs in dogs and cats as well.)

Reasons Why Your Pet’s Magnesium Levels Might Be High (Hypermagnesemia):

Kidney shut-down (oliguric renal failure), Addison’s disease, over-use of magnesium-containing supplements or laxatives can all increase blood magnesium. Urinary tract blockages can also cause higher-than-normal blood magnesium level. When a large amount of your pet’s muscle tissue is injured (necrosis), large amounts of magnesium are released. That can also cause your dog or cat’s blood magnesium levels to be temporarily elevated.

A hemolyzed blood sample can give falsely elevated magnesium level results.

Complimentary Tests:

BUN,   Creatinine, complete urinalysis all for evidence of kidney disease,   Free T4 level,     ACTH stimulation test for Addison’s Disease,   Blood calcium levelPTH levels


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