Hypercalcemia in Cats

Written by Small Door's medical experts

Calcium is an important part of your cat’s health, but too much calcium, also known as hypercalcemia, may become a toxic and emergent health situation. Read on to learn more about how hypercalcemia might come about, and how to identify the signs and symptoms of this condition in your own cat.

In this article

What is hypercalcemia in cats? 

Calcium is an essential mineral that aids healthy bodily functions and helps your cat’s body perform things such as muscle contraction, blood clotting, and nervous system regulation. However, too much calcium in the body can be toxic. 

Hypercalcemia, or elevated calcium, is what happens if your cat produces more calcium than normal. This occurs when the bones receive an incorrect message from another area in the body signaling them to make higher than normal levels of calcium. 

Hypercalcemia affects the entire body, but it will most drastically affect the kidneys, cardiovascular system, and nervous system.

Signs and symptoms of hypercalcemia in cats

Physical signs and symptoms that cats may exhibit when experiencing hypercalcemia include: 

  • Muscle weakness

  • Muscle twitching

  • Seizures 

  • Depression

  • Lack of appetite (also known as anorexia in cats)

  • Vomiting

  • Constipation

  • Increased thirst and urination

  • Heart arrhythmia (irregular heartbeat)

Causes of hypercalcemia in cats

There are several different causes for the development of feline hypercalcemia. These include: 

  • Idiopathic hypercalcemia: Idiopathic hypercalcemia means the underlying cause is unknown, and this is the most frequent type in cats. 

  • Chronic kidney failure: Another common cause of hypercalcemia stems from kidney failure. When the kidneys aren’t working properly, it will upset the balance of calcium and phosphorus in the body. It should be noted that hypercalcemia can cause kidney failure, and conversely kidney failure can cause hypercalcemia. 

  • Hyperparathyroidism: The parathyroid gland is responsible for controlling the levels of parathyroid hormone and calcium in the body. This gland works by affecting how calcium moves within the body (into and out of the bones, how calcium is absorbed within the gastrointestinal tract, and how much calcium is retained by the kidneys). When not functioning properly, it can overproduce calcium, which leads to the development of hypercalcemia. Hyperparathyroidism is a rare condition that occurs in cats. 

  • Granulomatous disease: A granulomatous disease is when a clump or mass of white blood cells forms, which can emerge from a bacterial, parasitic, or fungal infection. These clumps of white blood cells cause inflammation in the body, which affects the metabolism of vitamin D (which helps to absorb calcium), creating an elevated level of calcium in the bloodstream. 

  • Neoplasia: This is when calcium levels become elevated due to the presence of neoplasia (cancer). In cats, the most common forms of neoplasia associated with hypercalcemia are lymphoma and squamous cell carcinoma.

  • Ingestion of certain house plants: Some house plants, such as Cestrum diurnum (also known as the day-blooming jessamine), contain a substance similar to vitamin D that can cause a cat to develop hypercalcemia if ingested. Other plants that can cause hypercalcemia are Solanum malacoxylon (a South African nightshade) and Trisetum flavescens (yellow oat grass). 

  • Excessive vitamin D intake: Ingesting too much vitamin D can also cause hypercalcemia. Consult your veterinarian to make sure the nutrients and vitamins in your cat’s diet are properly balanced, and always check prior to introducing any new vitamins or supplements. 

  • Toxins: The ingestion of toxins, such as rodenticide (rat poison) containing cholecalciferol or anti-psoriasis topical skin creams containing calcipotriol, can lead to hypercalcemia. 

How common is hypercalcemia in cats?

Elevated calcium levels is a relatively common finding in routine blood work for cats, but not all elevated calcium levels necessarily mean your cat has true hypercalcemia. Calcium levels can be affected by many different factors, including lifestage, whether your cat has just eaten, and whether or not they are dehydrated

Diagnosing hypercalcemia in cats

Diagnosing hypercalcemia quickly can help improve your cat’s prognosis. Your veterinarian will first perform a thorough physical exam, assessing your cat’s heart and lungs, overall musculature, neurological status, and throat area to check for any palpable thyroid gland abnormalities. After performing a physical exam, the next step is to perform lab work. Some of the diagnostic tests your veterinarian may perform include: 

  • Complete blood count and blood chemistry: Your veterinarian will perform a complete blood count (also known as a CBC) and blood chemistry to evaluate your cat’s blood cells, platelets, and organ function. 

  • Ionized calcium: If your cat’s chemistry results showed high calcium levels, the next step is to perform an ionized calcium blood test. Ionized calcium testing measures the amount of the active part of the calcium cell a bit more precisely than the blood chemistry test. Things like excess fat in the bloodstream can affect the results of the chemistry test, but ionized calcium takes that into account, providing for a more accurate total. 

  • PTH and PTH-rP levels: Parathyroid hormone (PTH) and parathyroid hormone-related protein (PTH-rP) are hormones released by the parathyroid gland that are responsible for regulating the body’s calcium levels. Performing blood tests to measure the amount of both hormones can be helpful in diagnosing the underlying cause for your cat’s hypercalcemia. 

  • Radiographs: Radiographs may be taken so that your veterinarian can see whether there are any abnormalities, hidden tumors, or bone lesions in the body.

Treatment for hypercalcemia in cats

There are several different treatment methods for hypercalcemia. Depending on the severity of hypercalcemia, it may take one to several days for your cat’s calcium levels to normalize. The most common treatments are: 

  • Diet change: Often, the first line of treatment for hypercalcemia in cats is through therapeutic diet. There are several different varieties of veterinarian-prescribed diets that work to restore calcium levels back to normal. For instance, a diet for kidney disease helps the kidneys filter salt from the bloodstream, whereas a urinary diet to prevent calcium oxalate bladder stones helps restrict calcium levels in the blood. 

  • Prednisolone: Prednisolone, a glucocorticoid, is another common treatment for hypercalcemia. Prednisolone is helpful because it allows the kidneys to filter out more calcium from within the body. 

  • Intravenous (IV) fluids: Saline diuresis, or intravenous (IV) fluids, are used to help rehydrate the body and maintain blood flow. IV fluids work by adding fluids containing a specific balance of electrolytes directly to the bloodstream. This works faster than ingesting water or food, which has to go through the digestive tract prior to absorption within the body. 

  • Furosemide: Furosemide, a diuretic, removes excess calcium from the body. However, because this medication is a diuretic, only low doses are used in order to prevent dehydration. 

  • Bisphosphonates: Bisphosphonates are a group of medications that help promote cell turnover in the bones. Osteocytes are cells that make new bone, and osteoclasts are cells that dissolve bone. When osteoclasts dissolve bone, they release calcium into the bloodstream. Bisphosphonates are helpful for treating hypercalcemia because they suppress the osteoclasts from dissolving bone, therefore reducing the amount of calcium released into the blood. 

  • Parathyroid surgery: If the parathyroid gland is a contributing factor, your veterinarian may recommend surgical removal of abnormal parathyroid tissue.

Is there a cure for feline hypercalcemia?

Hypercalcemia is generally curable. If the hypercalcemia is due to an underlying disease, prompt diagnosis and treatment of the underlying issue will allow for resolution of the hypercalcemia.

Is feline hypercalcemia contagious for humans or other pets?

No, hypercalcemia is not contagious for humans or other pets or animals. 

What is the cost of treating hypercalcemia in cats?

Initial exam and diagnostics may cost several hundred dollars, whilst continued investigation can reach upwards of $1500. Cost of treatment will vary depending on the underlying cause found, but can be anywhere from $50 per month (if a prescription diet is sufficient to control the hypercalcemia), to many thousands of dollars if it is found to be secondary to cancer.

Recovery and management of hypercalcemia in cats

Hypercalcemia can have long-term effects on your cat, including soft tissue calcification and kidney damage. Regular monitoring of your cat’s calcium values may be necessary going forward.

Diet for hypercalcemia in cats

Your veterinarian may recommend your cat switch to a prescription diet specifically formulated to treat hypercalcemia. The specific type of diet is dependent on your cat’s lab work values and what their current needs are (for instance, they might require a diet that treats kidney disease or a diet that prevents urinary calcium oxalate crystals from forming). A wet-food-only diet is preferential, as the added moisture can help prevent urinary crystals, a byproduct of hypercalcemia, from forming. 

There are many diets to consider, but some changes that your veterinarian may recommend (depending on the cause) are:

  • Lightly salting food

  • Increasing fiber

  • Restricting dietary calcium

Your veterinarian will continue to monitor your cat’s calcium levels to see if dietary changes are working.

How long can a cat live with hypercalcemia?

The survival time for cats with hypercalcemia is variable, depending on the underlying case. With idiopathic hypercalcemia, cats can live normal lives with proper monitoring and lifestyle management (including diet, water intake, and medications as needed). With more pathogenic diseases, such as severe toxin exposure or cancers, the prognosis is poor and many cats succumb to the disease within days to months.

How to prevent hypercalcemia in cats

Not all causes of hypercalcemia are preventable. However, a few steps you can take to help prevent occurrences of hypercalcemia include eliminating any potential toxins from within your home and performing annual wellness monitoring lab work on your cat.

Is there a vaccine for feline hypercalcemia?

There is no vaccine for feline hypercalcemia at this time. 

Summary of hypercalcemia in cats

There are many causes of hypercalcemia in cats, some of which are benign and others which are more concerning.  In most instances, the early diagnosis of hypercalcemia starts with detection during annual or semi-annual blood work performed by your veterinarian. If you do notice changes at home which may be related to elevated blood calcium levels in your cat, it is very important to document what you're seeing and discuss these changes with your veterinarian. Early detection and proper diagnosis helps to improve outcomes and survival times in hypercalcemic cats.

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