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Overview:
Calcium is the most abundant mineral found in the body, approximately
99% is found in bone & the remaining 1% in
extra cellular fluid (fluid found outside of the cells and between
the cells in body tissues). It is essential for several functions
including providing strength to bones & teeth, cardiac function, proper
nerve impulses & muscle contractions, blood clotting. It is stored in
the skeleton & released as it is required. In combination with
phosphorous, it forms calcium phosphate, the dense, hard material of
bones & teeth.
Hypercalcemia is an abnormally high level of calcium in the blood
(greater than 12 mg/dl). Causes of
hypercalcemia include; cancer,
acute
or
chronic renal failure, primary hyperparathyroidism (a condition
where the parathyroid gland produces too much parathyroid hormone),
ingestion of certain houseplants (
hypervitaminosis D (excess levels of Vitamin D), generally caused by
over supplementation or rodenticide poisoning.
Some cases are idiopathic, meaning there is no known cause. Less common
causes include
Addison’s disease,
hyperthyroidism, granulomatous disease, certain cancers &
vitamin A toxicosis.
What
are the symptoms of hypercalcemia in cats?
There
may be no symptoms in mild to moderate cases of idiopathic hypercalcemia.
How
is it diagnosed?
Your veterinarian will
perform a complete physical examination of your cat & obtain a medical
history from you. Some tests he may wish to perform include;
-
Biochemical profile
which may or may not reveal high serum calcium concentrations & normal
to low serum phosphorous. BUN & creatinine may also be elevated due to
renal failure.
-
Complete
blood count.
-
Urinalysis.
High urine calcium can be indicative of parathyroidism. Low urine
calcium can be caused by
hypocalciuric
hypercalcemia.
-
Serum ionized
calcium (iCA):
Ionized calcium is calcium that is
freely flowing in your blood and not attached to proteins. It is also
called free calcium.
-
ECG
Obviously the goal is
to find out what is causing hypercalcemia & further investigative tests
will be required to determine this. These may include;
-
ACTH stimulation test for Addison's
disease: This test measures the ability of the adrenal glands to
respond to a hormone known as
adrenocorticotrophic hormone (ACTH)
which is made in the pituitary gland, travelling through the
bloodstream to the adrenal glands where it stimulates the secretion of
other hormones such as hydrocortisone from the cortex. The ACTH
stimulation test measures levels of cortisol in the blood before &
after an injection of synthetic ACTH.
-
Serum parathyroid hormone concentration:
To check levels of parathyroid hormone (PTH) in the blood.
-
Parathyroid hormone-related peptide (PTHrP)
is a protein secreted by some cancers.
-
X-Ray to look for calcium oxalate
uroliths & cancers.
-
Ultrasound of the parathyroid glands.
How is it treated?
Treatment depends on the severity & cause of hypercalcemia.
Some
treatments include;
-
Fluid
therapy to treat dehydration.
-
Loop
diuretics such as Furosemide (Lasix®)
to
increase calcium excretion from the kidneys.
Loop
refers to the drug's action on the loop of Henlé, a structure of the
kidney involved in reabsorbing water.
-
Glucocorticoids such as prednisone to decrease bone
resorption.
-
Sodium
bicarbonate helps decrease serum calcium levels by increasing the
alkaline level of the blood. This helps to shift the ionized calcium
into protein bound calcium, which is less harmful.
-
Cats
with primary hyperparathyroidism may require
surgery to remove the abnormal parathyroid
gland.
-
There
are other medications including; diphosphonates which
inhibit bone resorption, calcitonin which inhibits bone resorption &
mithramycin which inhibits osteoclastic bone resorption.
References:
The Feline Patient
Medline Plus Medical Encyclopedia
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