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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