Hypercalcemia In Cats: Causes, Symptoms, And Treatment

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Hypercalcemia in cats is a medical condition that occurs when the calcium levels in a cat’s blood are elevated beyond what is considered normal. Elevated blood calcium can occur as a primary problem such as in hyperparathyroidism, or it can occur secondary to another medical problem.

If your cat has been diagnosed with hypercalcemia, this article provides you with working knowledge you need to know about this mineral imbalance in cats.

What Are The Signs Of Hypercalcemia In Cats?

Many cats with mild hypercalcemia have no symptoms at all. Signs of hypercalcemia in cats occur when calcium is extremely elevated in the blood, or the calcium concentration in the blood has been elevated over time.

The clinical signs of hypercalcemia in cats are related to the cardiovascular system, the gastrointestinal system, the kidneys, and the neuromuscular system, and therefore can include:

  • Weakness
  • Excessive tiredness
  • Tremors or twitching
  • Loss of appetite (anorexia)
  • Hiding more, interacting with the family less
  • Constipation
  • Vomiting
  • Excessive drinking and urination due to kidney disease (polydipsia and polyuria)
  • Retinal blindness due to high blood pressure
  • Abnormal heart rate
  • Pale gums
  • Enlarged lymph nodes with lymphoma
  • Straining to urinate, increased trips to the litterbox, or bloody urine associated with calcium
  • Urinary bladder stones
  • Collapse or coma in severe cases

If you notice any of the above symptoms in your cat, call your veterinarian immediately, or contact a local emergency veterinary clinic, as severe hypercalcemia in cats is life threatening. If blood phosphorus and calcium levels are chronically elevated over time, it can cause irreversible organ damage.

What Causes Hypercalcemia In Cats?

Causes of hypercalcemia in cats

There are numerous causes of hypercalcemia in cats. 

The control of calcium inside the body is complex, and influenced by vitamin D and how the parathyroid hormone interacts with the stomach and intestines, bones, kidneys, and the parathyroid glands themselves.

Hypercalcemia in cats is either a primary problem with the parathyroid gland, a condition seen in Siamese cats, or it is secondary to another medical condition. One of the most common causes of hypercalcemia in cats is kidney disease, otherwise known as chronic renal failure. Other causes of hypercalcemia in cats include:

  • Addison’s disease (hypoadrenocorticism)
  • Destructive bone diseases
  • Hypercalcemia of malignancy (cancer)- most common in cats are lymphocytic leukemia, multiple myeloma, metastatic bone tumor, fibrosarcoma, squamous cell carcinoma
  • Aluminum intoxication
  • Certain fungal skin diseases
  • Rat bait toxicity (ingestion of Vitamin D rodenticide – no longer sold in the United States). If you suspect that your cat has consumed rat bait, call your local veterinarian or emergency veterinarian immediately, or call the Pet Poison Hotline.
  • Primary hyperparathyroidism (seen in siamese cats)
  • Idiopathic hypercalcemia seen in middle aged to older cats, no cause determined
  • Giving cats calcium, vitamin d, or calcitriol supplements
  • Mild elevations in blood calcium may be normal in growing cats

It is also helpful to know that calcium binds to albumin in the blood. If a cat is dehydrated, total calcium can be falsely elevated on blood tests, which is why measuring ionized calcium is required to get an accurate reading.

How Is Hypercalcemia In Cats Diagnosed?

Hypercalcemia in cats is diagnosed by running a sample of your cat’s blood through an analyzer that detects the level of calcium in the blood, or more accurately in the blood serum.

In specific, hypercalcemia in cats is defined as:

  • Total serum calcium > 10.5 mg/dL
  • Serum ionized calcium > 1.4 mmol/L

Blood tests can also detect additional diseases that may be causing hypercalcemia, such as kidney disease, cancer, or hormonal disorders.

Depending on which underlying cause of hypercalcemia is suspected, additional tests will be ordered. These tests may include urinalysis, x-rays, additional blood tests, abdominal ultrasound, and they can usually be done on an outpatient basis.

Radiographs (x-rays) are useful to look at the size and shape of the kidneys, look for any bladder stones, check for destructive bone tumors, or look for cancer in other parts of the body. An abdominal ultrasound may also be ordered to further image the organs in the abdomen, including adrenal glands, which cannot be seen on an x-ray.

An ultrasound of the parathyroid gland could also be ordered to look for tumors or enlargement of the gland. If cancer is suspected, specific cancer testing will be indicated, including biopsy of any tumors.

In addition to laboratory testing, your vet will rely on physical examination findings and your knowledge about your cat’s health and habits. Make sure to let your vet know if your cat is on any supplements, what food you feed, how long the problem has been going on, and what changes you notice in your cat.

This information is critical to help your vet nail down the cause of hypercalcemia in your cat.

How Is Hypercalcemia In Cats Treated?

Cat being treated at veterinarian

Severe hypercalcemia is considered a medical emergency and demands immediate care. 

A severely hypercalcemic cat is considered a medical emergency because of calcium’s impact upon the heart’s ability to contract and pump blood. Left untreated, severe hypercalcemia can be fatal. If your cat is diagnosed with severe hypercalcemia, she or he will likely be admitted to the veterinary hospital for in-patient care.

Treatment of choice for life-threatening hypercalcemia in cats is primarily fluids administered intravenously. Your cat will have a catheter placed into a vein, and then will be hooked up to fluids in the hospital.

The veterinary team will monitor your cat closely, and recheck blood calcium levels over time to ensure that blood calcium levels are coming down. They will also check your cat’s urine output levels to ensure that your cat is making urine normally, since kidney disease is commonly associated with hypercalcemia in cats.

Additional treatments that may be ordered to lower blood calcium include diuretics and steroids, such as prednisone.

Once your cat’s blood calcium levels and associated symptoms have been addressed, your vet will work with you to create a treatment plan to address whatever caused the hypercalcemia, if necessary. If there is a tumor in the parathyroid gland, then surgery is indicated. If hypercalcemia is due to kidney disease, then treatment of kidney disease is warranted, and so on and so forth.

How To Prevent Hypercalcemia In Cats?

There are many things you can do at home to help prevent hypercalcemia in your cat.

One easy thing you can do is ensure your cat gets excellent nutrition only feeding food that has been certified by AAFCO to be complete and balanced, either by formulation or feeding trial.

Second, don’t give any calcium, vitamin D, or calcitriol supplements to your cat unless directed to do so by a veterinarian. Excessive supplementation with these minerals and vitamins can upset your cat’s calcium balance.

Third, take your cat in for yearly veterinary visits and have your cat’s blood checked for high calcium. This is usually part of a larger blood panel that screens for many diseases. Don’t forget – cats age more quickly than humans. If your cat is older or has other heath challenges, get bloodwork run by your local veterinarian every 6 months.

Fourth, be mindful of what houseplants you keep in your home. Some houseplants, including Cestrum diurnum [the day-blooming jessamine], Solanum malacoxylon, and Trisetum flavescens) if chewed on may contain a Vitamin D type substance that can cause hypercalcemia. Keep cats away from these plants.

Fifth, if your cat has been treated in the past for hypercalcemia due to any reason, follow all your vet’s instructions closely – she or he will be your best guide to preventing any similar episodes in the future.

Frequently Asked Questions

What causes hypercalcemia in cats?

One of the most common causes of hypercalcemia in cats is kidney disease, otherwise known as chronic renal failure. Other causes of hypercalcemia in cats include Addison's disease, cancer, fungal diseases, Vitamin D toxicosis, and primary hyperparathyroidism. Idiopathic hypercalcemia with no known cause is also seen in middle aged to older cats.

Can hypercalcemia in cats be cured?

Hypercalcemia in cats can be be treated, however, without addressing the underlying cause of the elevated calcium levels in the blood, hypercalcemia will likely return.

What happens if hypercalcemia in cats is left untreated?

Hypercalcemia in cats, if left untreated, can be life-threatening. Hypercalcemia in cats can cause mineralization of internal organs, and negatively impacts the heart, the neuromuscular system, and can cause constipation and bladder stones.

About Dr. Sarah Wooten, DVM, CVJ

A 2002 graduate of UC Davis School of Veterinary Medicine, Dr. Sarah Wooten is a well known international speaker in the veterinary and animal health care spaces. She has 10 years experience in public speaking and media work, and writes for a large number of online and print animal health publications. Dr. Wooten is also a certified veterinary journalist, a member of the AVMA, and has 16 years experience in small animal veterinary practice. To learn more, visit drsarahwooten.com.

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