Hypercalcemia in Cats

Veterinarians run blood tests on cats for a wide variety of reasons. Sometimes, blood tests are intended to diagnose the cause of a cat’s illness. Other times, bloodwork is run for screening purposes, as part of an annual wellness exam or in preparation for anesthesia. 

Hypercalcemia is one of many conditions that can be diagnosed based on a cat’s bloodwork.  Some cases of hypercalcemia are mild, requiring minimal interventions and carrying a relatively good prognosis. Other cases are far more significant. Read on to learn more about hypercalcemia in cats. 

What Is Hypercalcemia in Cats?

Hypercalcemia is defined as abnormally high levels of calcium in the blood. 

Under normal circumstances, your cat has systems in place that regulate blood calcium. Parathyroid hormone, calcitriol (the active form of vitamin D), and calcitonin (a hormone released by the thyroid gland) all play a role in regulating blood calcium.

Hypercalcemia can be caused by a wide variety of conditions, which can affect any of these calcium regulatory systems. Hypercalcemia is most common in older cats, but it can affect cats of any age. 

Hypercalcemia vs Hypocalcemia

Hypercalcemia refers to increased blood calcium. “Hyper” is a prefix that means excessive, and “-calcemia” is a root wood that refers to blood calcium. Therefore, a cat with hypercalcemia has excessive calcium in the blood. 

You may also hear veterinarians refer to hypocalcemia. “Hypo” means low or below normal. Therefore, a cat with hypocalcemia has abnormally low levels of calcium in the blood. 

It’s easy to confuse these words, especially if your veterinarian is speaking quickly. If you’re unsure which condition your veterinarian is describing, ask for clarification.

Causes of Hypercalcemia in Cats

Hypercalcemia in cats can have many potential causes. However, the three most common causes are: 

• Kidney disease: The kidneys play an important role in regulating the levels of calcium and other substances in the blood. When the kidneys aren’t working correctly, calcium can build up to abnormally high levels. 
• Malignant cancer: Some cancers, including lymphoma and squamous cell carcinoma, have been shown to cause hypercalcemia in cats. 
• Idiopathic hypercalcemia in cats: This is one of the most common causes of hypercalcemia in cats. “Idiopathic” means hypercalcemia arises spontaneously, with no known cause. These cats do not have any underlying diseases that can be found as a cause of their hypercalcemia, despite extensive testing. 

Less common causes of hypercalcemia in cats include: 

• Adrenal hormone insufficiency
• Destructive bone disease (infection, bone cancer)
• Fungal infection 
• Hyperparathyroidism
• Nutritional imbalances
• Vitamin D toxicity (caused by rat poison)

Genetics doesn’t seem to play a role in hypercalcemia. No specific breeds have been found to be at higher or lower risk of hypercalcemia. 

Hypercalcemia in Cats Symptoms

Clinical signs of hypercalcemia can vary widely. Some cats are completely asymptomatic, while others are very sick by the time their condition is diagnosed. 

Signs of hypercalcemia in cats may include: 

• Decreased appetite
• Vomiting
• Diarrhea
• Lethargy
• Weakness
• Dehydration
• Increased thirst
• Increased urination
• Abdominal pain
• Muscle spasms
• Seizures

It’s important to note that the signs of hypercalcemia mimic the signs of many other conditions. This condition can’t be diagnosed on clinical signs alone. 

Diagnosing Hypercalcemia in Cats

Hypercalcemia is diagnosed based on a blood test. If your cat is showing vague signs of illness, your veterinarian will likely recommend blood tests to evaluate your cat’s health. In a cat with hypercalcemia, blood tests will show an abnormally high blood calcium level. 

Not all elevated calcium levels are clinically significant. Calcium levels can fluctuate over time, and they may be briefly elevated but then return to normal. If your cat’s blood calcium is elevated on screening bloodwork, your veterinarian will probably perform further testing to be sure the elevated calcium level is significant. This may involve rechecking blood tests a few days later or sending your cat’s blood to a reference laboratory, which can perform more specialized tests. If your cat’s blood calcium elevation is found to be significant, your veterinarian will diagnose your cat with hypercalcemia. 

After receiving a hypercalcemia diagnosis, the next step is figuring out the underlying cause. Your veterinarian will recommend further tests to look for potential causes of hypercalcemia. Further testing may include additional blood tests, urinalysis (to check kidney function), imaging (to look for cancer), and other diagnostics. It’s important to determine the cause of your cat’s hypercalcemia (if possible), because this determines the best treatment for your cat. 

Hypercalcemia in Cats Treatment

If your cat is very sick with hypercalcemia, your veterinarian will take steps to lower your cat’s blood calcium levels quickly. This may include intravenous (IV) fluids, diuretics (to encourage calcium elimination in the urine), and other medications. 

Next, your veterinarian will shift to long-term treatment strategies. 

If possible, your veterinarian will aim to control the underlying cause of your cat’s hypercalcemia. This is the best treatment for hypercalcemia. Treatment may involve fluid therapy and dietary changes for kidney disease, chemotherapy or surgery for cancer, or other treatments. 

If the underlying cause of your cat’s hypercalcemia cannot be determined and/or treated, your veterinarian will start your cat on long-term medications. These medications are intended to reduce your cat’s blood calcium levels. The efficacy of these medications can vary, and these medications may cause significant side effects. Therefore, it’s always best to control the underlying cause of hypercalcemia, if possible. 

What to Feed a Cat with Hypercalcemia

Your veterinarian will recommend the best diet for your cat. There is no single best cat food for hypercalcemia. 

If your cat’s hypercalcemia is caused by an underlying disease, your veterinarian will probably recommend a diet to help manage the underlying disease. 

If your cat has idiopathic hyperthyroidism, your veterinarians may recommend a diet that is low in calcium. Diets that are low in carbohydrates, high in protein, and/or high in fiber have also been recommended to reduce hypercalcemia, although research in this area is limited and opinions vary. 

Cost to Treat Hypercalcemia in Cats

The cost to treat hypercalcemia will vary, depending on the underlying cause of your cat’s condition. 

The initial diagnostic testing for hypercalcemia can cost anywhere from a few hundred dollars to over $1,000, depending on your cat’s individual case. 

If your cat has mild hypercalcemia that can be addressed through a dietary change, the cost of treatment and monitoring may be as low as several hundred dollars per year. If your cat has lymphoma or another malignant cancer, treatment may cost several thousand dollars. 

Your veterinarian can provide a more educated estimate of treatment costs once they have determined the underlying cause of your cat’s hypercalcemia.

How to Prevent Hypercalcemia in Cats

Given the wide variety of conditions that may cause hypercalcemia, there is no way to definitively prevent this condition. However, there are steps you can take to reduce your cat’s risk, such as:

• Feed a well-balanced diet. An imbalanced diet is one potential cause of hypercalcemia.
• Keep your cat away from toxins and human nutritional supplements, both of which may impact blood calcium levels. 
• Follow your veterinarian’s recommendations for wellness exams and bloodwork monitoring. Most veterinarians recommend annual bloodwork for cats. Screening bloodwork can aid in the early diagnosis of hypercalcemia, in addition to many other diseases. 
• Seek veterinary care if you notice weight loss, lethargy, or other signs of illness.

While there’s no way to definitively prevent hypercalcemia, paying attention to your cat’s health and following your veterinarian’s recommendations can help reduce the risk.