Hypercalcemia in Cats


by Arnold Plotnick MS, DVM, ACVIM, ABVP

Calcium is an essential nutrient, however, excessive blood levels can have serious consequences.  Catnip’s medical editor explains the causes of – and concerns about – too much calcium

Calcium plays an essential role in maintaining a healthy body in humans and animals.  Too much of a good thing, however, can be dangerous, and this is definitely true for calcium.  Discovering an elevated serum calcium level in cats is a fairly common finding in veterinary medicine.  A variety of treatments are available that will readily bring an elevated calcium back into the normal range, but treating with medication should not be the primary approach.  Because the most  effective treatment is to address the underlying cause, our initial approach  to hypercalcemia  (elevated  serum calcium) is to search for the origin.  Once we find the cause (or should I say if we find the cause, because sometimes it can be tricky), we can prescribe the proper treatment.

“Most cat owners wouldn’t know that their cat has an elevated calcium level”, says Dr. Michael Stone, board-certified internist at the Cummings School of Veterinary Medicine at Tufts. “Cats tend to be more resistant to the clinical consequences of hypercalcemia, and in many cases, cats can have a fairly high calcium level and appear totally normal.”  Most of the reported signs are vague and non-specific, such as poor appetite and lethargy. (See Sidebar 1)  Increased thirst and urination are occasionally reported.  Elevated calcium levels can sometimes lead to the development of calcium-containing bladder stones, and cats may show signs such as straining to urinate and blood in the urine.  Very high calcium levels often lead to gastrointestinal symptoms (such as vomiting and constipation) or neurological signs (such as muscle twitches and spasms, or seizures).  Left untreated, the excess calcium can combine with phosphorus in the bloodstream, forming calcium phosphate. Calcium phosphate will deposit in a variety of tissues throughout the body, especially the kidneys, gastrointestinal tract, cardiac muscle, skeletal muscle, tendons, and ligaments. These mineral deposits can lead to tissue damage, including initiation of (or acceleration of pre-existing) kidney disease, decreased cardiac function, and abnormal heart rhythms.

There are many causes of hypercalcemia.  (Sidebar 2).The most common cause of high calcium is chronic renal failure.  Not all cats with renal failure will have high serum calcium, and those that do tend to have only mild elevations.  Fortunately, diagnosing chronic renal failure is easily accomplished via routine blood and urine tests.

Hyperparathyroidism is a well-documented cause of high calcium in cats.  The parathyroids are small glands located near the thyroid gland in the neck.  These glands secrete hormones that regulate the serum calcium level, the main one being parathyroid hormone (PTH).   Some cats, as they age, may develop a benign tumor involving one of the parathyroid glands.  This tumor will secrete excessive amounts of PTH, causing the calcium to rise, often to dangerous levels.    A few cases can be diagnosed by carefully feeling the neck and identifying a small nodule where the parathyroid glands reside.  In most instances, a diagnosis is achieved by measuring the level of PTH in the serum.  An elevated level confirms the diagnosis, although some cats with hyperparathyroidism will have normal PTH levels, confounding the diagnosis.

Neoplasia (cancer) is another common cause of high calcium. “After renal failure, cancer is probably the second most common cause of elevated calcium in the cats we see” notes Dr. Stone.  While any cancer can theoretically cause elevated calcium levels, the most common types are lymphosarcoma, squamous cell carcinoma, multiple myeloma, and mammary carcinoma.  In most cases, diagnosing the cancer is relatively straightforward, however, the diagnosis can sometimes be elusive, especially in the case of lymphosarcoma.    Calcium levels are high in some cases of cancer because the malignant cells are secreting a protein that is very similar to PTH, the hormone that regulates serum calcium levels.   In fact, this protein is called parathyroid hormone-related protein, abbreviated PTH-rp.   In normal animals, PTH-rp  levels are not detectable.  In cats, PTH-rp is not a very sensitive marker for cancer; some cats with cancer-associated hypercalcemia may have undetectable blood levels of PTH-rp. However, the PTH-rp test is very specific, meaning that if the levels of PTH-rp are elevated, a diagnosis of cancer is certain.

Granulomatous diseases are usually infectious diseases that result in a characteristic type of inflammatory response by the body.  Most of these diseases are fungal, but bacterial, viral, and parasitic disorders can cause granulomatous inflammation as well.  The mechanism by which these diseases cause elevated calcium levels is complex, and has to do with altered vitamin D metabolism.  Diagnosis of granulomatous diseases is usually straightforward and may involve cultures, blood tests, and other common diagnostic procedures.

Osteolytic diseases – disorders in which bone is being destroyed – is an uncommon cause of high calcium in cats.  Occasionally, tumors will invade or spread to the bones, or an infection will occur in a bone that causes enough bony destruction that the calcium will become elevated.  Again, this is quite rare.  X-rays will often reveal the bony destruction.

Vitamin D toxicosis is another uncommon cause of high calcium levels in cats, and could occur theoretically if a cat was deliberately oversupplemented with vitamin D.  A few years ago, a new type of rat and mouse poison was introduced on the market.  This new rodenticide had calcitriol as its active ingredient.  Calcitriol is the active form of vitamin D, and it killed rats and mice by elevating their calcium levels.  Cats that ate it, or ate rodents poisoned by it, would develop hypercalcemia.  Fortunately, these products are no longer widely available, at least in the U.S.    A more common cause of vitamin D toxicity is ingestion of calcipotriene, a substance very similar to calcitriol that is found in a topical preparation used to treat psoriasis in people.  To date, this has only been reported in dogs.  Cats, apparently, are smart enough to not eat this ointment. 

Hypoadrenocorticism (also known as Addison’s disease) is a condition where the adrenal glands produce inadequate amounts of certain hormones.  Affected animals will often have elevated calcium levels, although the mechanism behind this remains unclear.  “Addison’s disease is uncommon in dogs, and is even less common in cats.  I would venture that most practicing veterinarians never see a case of feline Addison’s disease in their career”, says Dr. Stone.   Diagnosis of Addison’s disease is achieved by measuring serum cortisol levels before and after injecting the cat with a hormone called ACTH.  A normal cat will show a significant increase in serum cortisol levels after the injection.  A cat with Addison’s disease will not.

A common cause of high calcium, and one that should not be overlooked, is a spurious lab result, i.e. an error in measurement by the laboratory.   Diagnostic laboratory capabilities have gotten much more sophisticated over the years, and the quality control in these labs has improved markedly.  No laboratory is 100% perfect, however, and mistakes do occur.  I once ran routine senior bloodwork on a 13 year-old Somali named Rudy, and the calcium came back at 19 mg/dl, a shockingly high number.  With Rudy showing no clinical signs of illness at all, I had the laboratory re-run the test on a new specimen.  The new calcium result was 10.8 mg/dl, which was totally normal. 

In some cases, after an extensive diagnostic workup, no cause for the hypercalcemia is ever revealed.  Since the early 1990’s, cases of unexplained hypercalcemia have become increasingly more apparent, and has been termed idiopathic hypercalcemia (IHC).  “Idiopathic” means that there is no known cause.  IHC is turning out to be one of the most common causes of hypercalcemia in cats. 

As stated earlier, treatment of hypercalcemia is based on the cause.   For example, hyperparathyroidism is treated by surgically removing the overactive parathyroid gland; cancer is treated with surgery, radiation, or chemotherapy; Addison’s disease is treated by administering the deficient hormone(s).   If the cause cannot be determined, as in IHC, then a variety of interventions can be attempted. 

Elevated calcium levels can sometimes be restored to normal by changing the cat’s diet.  High fiber diets, diets designed for cats with renal failure, and diets designed to prevent calcium oxalate bladder stones have all been shown, in various studies, to normalize the calcium level in some hypercalcemic cats.  If, after feeding a new diet, the calcium level remains elevated, treatment with glucocorticoids should be considered.  Most cats with IHC respond favorably to glucocorticoid administration.  Ideally, the dose should be tapered to the lowest dose that controls the hypercalcemia, to minimize any adverse effects (such as diabetes). As an alternative to glucocorticoids, cats can be given biphosphonates, a class of drugs designed to prevent the loss of bone mass.  Biphosphonates are often given to women to treat or prevent osteoporosis. They are very effective at lowering the level of calcium in the blood. 

Determining the cause of hypercalcemia can be a challenge.  A careful evaluation of the history, physical exam findings, and various laboratory tests often leads toward a logical path to a diagnosis.  The best chance of successfully treating hypercalcemia in cats is to eliminate the underlying cause.

Sidebar 1
Clinical signs of hypercalcemia in cats
Decreased appetite
Increased thirst and urination
Changes in urinary behavior (straining, increased frequency, blood in urine)

Sidebar 2
How Catnip’s medical editor remembers the causes of hypercalcemia in cats
In veterinary school, we are asked to memorize thousands of fact and figures.  It would be impossible to do this without mnemonic devices, those cute little learning aids that help us remember important facts.  There are several mnemonic devices for the causes of hypercalcemia in animals. Since Catnip is a family publication, I’ll share a non-racy one:  GOSH DARN!
G = granulomatous diseases
O = osteolytic disorders
S = spurious laboratory result
H = hyperparathyroidism
D = vitamin D toxicosis
A = Addison’s disease
R = chronic renal failure
N = neoplasia (cancer)

As I go through my list, if none of the letters explain the cause of the cat’s high calcium, then the cat likely has idiopathic hypercalcemia - the calcium is high for no discernable reason.
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Top 20 Internet Cat Videos of 2011

We've gathered together our 20 favorite cat videos from 2011 that we posted throughout the year on our Manhattan Cat Specialists' Facebook Page. Without further ado:

Oskar the Blind Kitten's First Toy

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Plastic Cat Fortress

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Cat Ruins Video

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Dr. Plotnick's Top 13 (Educational) Feline Blog Posts of 2011

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13) The Cat Age to Human Age Comparison (Part Three) - A New Chart Helps Pet Parents Calculate Their Cats' Age in Relation to Human Years

12) What We Tell Our Clients When their Cat is Diagnosed with Ringworm - Despite the name, ringworm is not a “worm”.  It is a fungal infection (dermatophytosis) of the hair and skin.  It is also one of the few feline infectious diseases that can be transmitted from cats to humans.  Cats that test positive for ringworm need some kind of treatment.  Treatment plans may vary somewhat for each individual cat, but they all involve three basic steps – topical therapy (bathing) with some type of shampoo, oral medication, and environmental decontamination.

11) Tropic of Cancer (a.k.a. lymphosarcoma. a.k.a. lymphoma) - I see a lot of cancer in my cat practice.   A major reason is that cats are living longer than ever before.  Now that they’re living to 17, 18, (and even longer), they’re living long enough to develop cancers that we never saw when they died at 12 or 13.  Another reason is that major medical advances have given us the technology to detect cancers that previously went undiagnosed.  An increased awareness of cancer, coupled with more sophisticated technology, has allowed veterinarians to become pretty adept at making the dreaded diagnosis. The diagnosis of cancer in a beloved cat can be devastating.  However, it is important to realize that, as in human cancers, many types of cancer in cats can be treated, managed, and sometimes even cured.   

10) Heart Murmurs: What’s the Scoop? - Everyone has heard of heart murmurs, but not everyone knows exactly what they are, and what their significance may be. I’m hoping this blog post can help.  

9) Hot-Weather Tips for our Cat & Dog Companions - When summer arrives, it is very important that we take the proper precautions when dealing with our pets. Here are a few important tips and facts that should help protect our furry friends.

8) Language Barriers - I run an all-feline veterinary hospital, and we have a fairly large Japanese client base. This is not by accident. One of my technicians, Hiromi, is Japanese, and she made it clear to me when I hired her 8 years ago that she would like to actively help me cultivate a Japanese clientele. In speaking with her cat-owning Japanese friends and acquaintances, Hiromi has heard countless tales of frustration, as they described the difficulty in explaining exactly what it is about their cat that had them worried, as well as their inability to fully understand what the doctor had told them.

7) First Aid and Your Kitten: What to Do in an Emergency - Most kittens endure kittenhood relatively unscathed. A few, however, deplete several of their nine lives in the course of growing up. Knowing the principles of first aid can be invaluable in seeing that your kitten survives that turbulent first year of life.

6) First Aid and Your Cat: What to Do in an Emergency - If you came home from work and found your cat having convulsions, paralyzed, or bleeding, would you know what to do?  April is "Pet First-Aid Awareness Month". The American Animal Hospital Association, (AAHA) states that 1-out-of-4 pets would survive an accident or illness if pet owners were familiar with and capable of providing first aid when necessary. Owners that are aware of proper life saving techniques and how they apply to our pets are better equipped to handle emergencies as they arise. 

5) Why You Should Spay or Neuter Your Cat - Cat overpopulation is a very serious problem in the United States. There are simply too many cats and not enough people to care for them. Responsibility is the key to cat ownership, and a major part of that responsibility is guaranteeing that your cat doesn’t reproduce.  Neutering and spaying are two of the most commonly performed elective procedures.  Not only do they help curtail cat overpopulation, they also bring many health and behavior benefits to both you and your cat.

4) Top 5 Healthy Cat Treats - Cats require a nutritionally complete and balanced diet to live an active, healthy life. Life is meant to be enjoyed, however, and every now and then it’s OK to toss your cat a tasty treat.

3) Early Spaying and Neutering in Cats. Get ‘em while they’re young - Every year in the U.S., animal shelters and humane organizations euthanize millions of homeless and unwanted dogs and cats. Spaying and neutering has to remain the cornerstone of any program designed to reduce overpopulation of dogs and cats. In my practice, clients will often bring me a kitten for examination and vaccination. Our protocol is typical for most veterinary practices: we vaccinate around 8 or 9 weeks of age, and again at 11 or 12 weeks of age, and once more at 15 or 16 weeks of age. Then, at 24 weeks of age, we neuter or spay. This protocol of spaying and neutering around 6 months of age has been the professional standard for years. This posed a problem for shelters, however. 

2) How Pet Owners Can Best Help Veterinarian Make their Diagnoses - Veterinarians are faced with a variety of diagnostic challenges on a daily basis. The ability for a veterinarian to obtain a detailed and complete history is our most important diagnostic tool. When accurately interpreted, this information lays the groundwork for a logical diagnostic and therapeutic plan, and may prevent unnecessary diagnostic testing and needless discomfort to the patient and cost to the owner. 


1) Anatomy of the Feline Mouth - As a cats-only practitioner, I don’t mind when people say that I’m looking down in the mouth, because the feline mouth is fascinating. Cats use their mouths for a lot of things – eating, drinking, grooming, and communication. Although cats breathe mainly through their nose, the mouth provides an additional passageway for air to enter the lungs.


Make sure to check out the Top Fun Feline Blog Posts of 2011

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Number 7) 10 Best Talking Cat Videos
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Number 5) The New York City Bodega Cat
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Number 4) 20 Close-Up Photos of Cat Tongues
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Number 3) Must Re-home - Urgent!
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Number 2) Dr. Plotnick's Visit to Katten Kabinet in Amsterdam
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Number 1) Dr. Plotnick's Cat Expedition in Istanbul, Turkey
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Make sure to check out the Top 13 (Educational) Feline Blog Posts of 2011

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Know the facts. 99% of cats live a more lavish lifestyle than 99% of the top 1% of humans. OCCUPY CATS! Get Your Cats Spayed or Neutered.

SEE: Why You Should Spay or Neuter Your Cat

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