Hypercalcemia in Cats: Causes, Symptoms, and Treatment

Katelynn Sobus / Cats.com

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.

Other Names: Excess Calcium in the Blood in Cats

Common Symptoms: Weakness, collapse, tremors or twitching, increased thirst and urination, poor appetite, constipation, vomiting, pale gums, urinary bladder stones.

Diagnosis: Bloodwork, urinalysis, x-rays, abdominal ultrasound

Requires Ongoing Medication: Yes

Vaccine Available: No

Treatment Options: Treatment depends on the underlying cause and severity. Severe hypercalcemia typically requires hospitalized care. More mild cases may be addressed with medical management.

Home Remedies: No

What Are the Signs of Hypercalcemia in Cats?

Many cats with mild hypercalcemia have no symptoms at all. In fact, it isn’t uncommon for a mild hypercalcemia to show up on wellness screening or preoperative labwork in an otherwise apparently healthy looking cat.

Signs of illness related to 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?

There are numerous causes of hypercalcemia in cats. Katelynn Sobus / Cats.com

The control of calcium inside the body is complex, and influenced by vitamin D and how parathyroid hormone interacts with the stomach and intestines, bones, kidneys, and the parathyroid glands themselves. The parathyroid glands are very tiny glands located on or near the thyroid glands in the neck.

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 chronic kidney disease, which may develop further over time into renal (kidney) failure. Other causes of hypercalcemia in cats include:

• Addison’s disease (hypoadrenocorticism)
• Destructive bone diseases
• Hypercalcemia of malignancy (cancer)- most common in cats are lymphoma, 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 (IHC) seen in middle aged to older cats, no cause determined
• Giving cats calcium, vitamin D, or calcitriol supplements
• Nutritional imbalance (where the ratio of calcium to phosphorus in the diet is too high)
• 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.

The corrected calcium equation often used in dogs to factor in the albumin level’s relationship to the calcium level also cannot be used in cats. Their physiology is different enough from dogs that this equation is not considered reliable.

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

Of the two, only ionized calcium is considered reliable to make a diagnosis of hypercalcemia in cats. This is because total calcium is still impacted by calcium bound to protein (albumin) while ionized calcium is not. Total calcium can be considered as a screening test, especially since it is included with many common lab work panels. But if the total calcium is high, your vet will often recommend following up with an ionized calcium to see if a true disorder is present.

Blood tests can also detect additional diseases that may be causing hypercalcemia, such as kidney disease, abnormalities seen with some cancers, and some related hormonal disorders. If a total calcium is high and an ionized calcium is being checked, it can be common to check parathyroid hormone (PTH) levels to help rule in/out hyperparathyroidism.

PTHrp, which stands for parathyroid hormone related protein, is expressed by certain types of cancers. If PTHrp is found, it can highly suggest that a cancer of some kind is related to the calcium elevation. If PTHrp is not found, this does not fully rule out cancer as it is not found with all cancers. Either way, this test can help guide next diagnostic steps when determining the cause of hypercalcemia.

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, and look for any bladder stones that high calcium could cause. X-rays can also be used to screen for some tumors.

An abdominal ultrasound is more useful to further image the organs in the abdomen. Signs of mineralization of tissues and stones can also be seen on ultrasound. Some tumors or cancerous changes may be present within tissues without actually increasing their size or appearance on an x-ray, but an ultrasound is highly sensitive to detect these changes. Ultrasound is also the best way to evaluate lymph nodes within the body, which is very important when screening cats for lymphoma.

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?

Severe hypercalcemia is considered a medical emergency and demands immediate care. Kirsten McCarthy / Cats.com

Severe Hypercalcemia

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 prednisolone.

Once your cat’s blood calcium levels and associated symptoms have been addressed and stabilized, your vet will work with you to create a treatment plan to address whatever caused the hypercalcemia.

A parathyroid gland tumor, while rare, would need to be surgically removed if found to be the cause. If more advanced kidney disease is related to a severe elevation, the kidney disease itself must become a focus of continued therapy.

Mild to Moderate Hypercalcemia

In many cases, hypercalcemia is found incidentally on lab work. This may be lab work even performed for wellness screening in an otherwise healthy looking cat. Sometimes, a cat may be losing weight or showing signs of illness and lab work is performed that shows a calcium elevation.

These elevations are usually mild, but that doesn’t mean they should be ignored. Over time, if the underlying cause is not determined, the elevations may continue and over time contribute to more serious disease.

Nutritional therapy is often one first line approach to therapy for hypercalcemia in cats, especially if it is related to chronic kidney disease or is an idiopathic hypercalcemia (meaning other causes have been ruled out and the cause for the high calcium is undetermined).

A diet with a calcium phosphorus ratio of less than 1.4:1 (but still higher than 1:1) has been proposed as one therapy approach with diet.

Other dietary approaches may be with prescription diets designed to prevent calcium-based bladder stones or with prescription kidney disease therapy diets. Their use may depend on a veterinarians experience and success in using them for this purpose and a cat’s response.

Fiber is another proposed way to address hypercalcemia with diet. Fiber may help decrease the transit time for digested food, reducing how much calcium is absorbed into the bloodstream and also bind dietary calcium inside the gut.

But not all fiber is created equal. Chia seeds specifically have been studied in cats with hypercalcemia. When fed at about 1-2g per day, studies have shown calcium levels go down in both cats with kidney disease and idiopathic hypercalcemia. Chia seeds have been shown to be successful even when other dietary therapy has not been.

In terms of medications used to address hypercalcemia, glucocorticoid steroids like prednisolone have been one of the most common choices. Glucocorticoids reduce intestinal absorption of calcium, reduce reabsorption by the kidneys, and reduces mobilization from bones. Prednisolone can help bring calcium levels down in a short period of time. The downside is that over time steroids can increase the risk for development of diabetes and in cats at risk, progressive heart disease.

Alendronate, a medication that reduces calcium mobilization from bone stores, has shown promise as a potentially safer long-term medication option. One study in 2022 showed cats tolerated the medication well compared to reports from humans, though further studies are still needed.

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. If possible and the information is available for your cat’s diet, check the calcium to phosphorus ratio. An ideal ratio should be at least 1:1 but according to some studies, still less than 1.4 to 1. This is important, both for avoiding excess calcium or excess phosphorus, but is not information that is readily available. AAFCO’s new labeling requirements to be implemented by 2030 may be helpful in providing better information.

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 10 years of age or 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.