Hypercalcemia in Cats

What Is Hypercalcemia in Cats?

Hypercalcemia means that a cat's calcium level is higher than normal in the bloodstream. Calcium is an essential mineral that keeps a cat's bones strong and helps with muscle contraction, the clotting of blood, and other essential functions. The amount of calcium in a cat's body is closely regulated, so only the amount needed is normally available at any given time. However, certain medical conditions can cause the calcium level to become too high.

There are many possible causes for a cat's calcium level to be elevated. Some may be lifelong issues, while others are only temporary. If a cat has significant hypercalcemia that persists, then the extra calcium will build up in multiple organs, leading to mineralization. Organs that have mineralization are unable to function properly.

For instance, high calcium can prevent the muscles throughout the body from contracting, such as within the heart, limbs, and gastrointestinal tract. A cat with hypercalcemia may develop weakness, muscle wasting, impaired heart function, and a decreased appetite, as well as other symptoms. Hypercalcemia can be life-threatening because it can lead to kidney failure, irregular heartbeat, chronic gastrointestinal issues, and inability to walk.

Symptoms of Hypercalcemia

Cats with mild hypercalcemia often do not show signs of illness. But if a cat’s total calcium level rises over a certain level, then these symptoms may be seen:

Neuromuscular

• Lethargy

• Muscle wasting

• Muscle tremors or twitching

• Inability to walk

• Seizures

Gastrointestinal

• Decreased appetite

• Anorexia

• Constipation or diarrhea

• Vomiting

Renal/Urinary tract

• Increased thirst and urination

• Dehydration

• Vomiting

• Decreased appetite

• If bladder stones form in the urine due to calcium buildup, a cat may have blood in the urine and strain to urinate small amounts.

Cardiac

• Heart arrhythmia (abnormal heartbeat)

• Weakness

• Collapse

The above symptoms are usually seen at home by pet parents and then reported to the veterinarian during an appointment. However, some cats with hypercalcemia have no symptoms, and the only way to detect this medical condition is for your veterinary professional to measure your cat's calcium level with a blood test during an annual exam.

Causes of Hypercalcemia

Cats can develop hypercalcemia due to several causes:

• Idiopathic hypercalcemia: This medical condition is the most common cause.  It means that after running numerous diagnostic tests, no cause for a cat's elevated calcium level can be found and all known medical conditions have been ruled out.

• Renal (kidney) disease: When a cat has severe kidney disease, the kidneys can no longer function properly, which leads to a cascade of unfortunate events. Ultimately, mineral deposits form within soft tissue, including the kidneys, leading to even poorer kidney function.

• Hypercalcemia of malignancy: Some cancers release a protein that stimulates the breakdown of bone tissue, allowing calcium to be released from the bone into the bloodstream, where it builds up.

The two most common cancers that cause hypercalcemia in cats are lymphoma and squamous cell carcinoma. Other types of cancers such as mammary cancer, cancer within the anal sac, and multiple myeloma are less common.

• Primary hyperparathyroidism: Occasionally a benign or cancerous mass can develop in one or more parathyroid glands in a cat’s neck. A benign mass called a parathyroid adenoma is the most common cause of primary hyperparathyroidism in cats. When a mass is present within the parathyroid gland, it overproduces parathyroid stimulating hormone (PTH) that controls calcium levels in the bloodstream. Whether it is benign or cancerous, excess PTH leads to resorption of bone and a release of extra calcium into the bloodstream, causing hypercalcemia.

• Hypoadrenocorticism: This endocrine disorder, also known as Addison’s disease, is very rare in cats and develops when the adrenal glands are unable to produce glucocorticoids (steroids) and mineralocorticoids. Cats with this condition are typically lethargic, lose weight, and have anorexia. Hypercalcemia can occasionally be seen in the bloodwork of a cat that has hypoadrenocorticism.

• Vitamin D toxicosis: Too much vitamin D can cause hypercalcemia. Cats can consume a toxic dose of the vitamin through diet or by ingesting rodenticide, a day-blooming jasmine plant, or eczema cream.

• Transient hypercalcemia: This is when a cat has dehydration due to lack of water or gastrointestinal symptoms (vomiting and diarrhea). Once the dehydration and underlying cause are corrected, the calcium level returns to normal in most cases. Further diagnostics or treatment are not needed unless GI symptoms recur.

• Fungal infections: Cryptococcus neoformans, blastomycosis, histoplasmosis, and bacterial infections caused by atypical mycobacterium or Actinomyces spp. can cause hypercalcemia in cats.

How Veterinarians Diagnose Hypercalcemia in Cats

Depending on the cat and their health history, a veterinarian may use one or more of the following diagnostics to determine hypercalcemia in cats and how to treat it.

• Physical and rectal exams: A veterinarian can check for muscle wasting, muscle tremors, lethargy, decreased mobility, cancerous masses, enlarged lymph nodes, and an irregular heart beat.

• Bloodwork: A blood cell count (CBC), electrolytes, and chemistry panel that includes a total calcium level.  If the total calcium level is elevated, an ionized calcium level is recommended to confirm if the hypercalcemia is clinically significant.

• Urinalysis: This is done to screen for kidney disease.

• Fine needle aspiration: A small needle is used to obtain cells from an enlarged lymph node to screen for lymphoma and other forms of cancer.

• Parathyroid hormone assay: This blood panel helps test for hyperparathyroidism by measuring the amount of parathyroid hormone (PTH) in the bloodstream. If the level of PTH is elevated in a cat that has hypercalcemia, then primary hyperparathyroidism is likely the cause of the elevated calcium level.

• Parathyroid Hormone-Related Protein (PTHrP) Assay: This is another blood test that measures the amount of parathyroid hormone-related protein in the bloodstream. If a hypercalcemic cat has elevated PTHrP, then cancer is likely present and the cause for the hypercalcemia.

• Ultrasound of the neck: A board-certified radiologist examines the parathyroid glands and thyroid gland to see if a tumor is present.

• Abdominal ultrasound: It may be needed to screen for cancerous masses in the abdomen that can cause hypercalcemia.

• Advanced imaging: A CT scan or MRI screens for a cancerous mass that could be the cause of a cat's hypercalcemia.

• Bone marrow cytologic exam: This exam reviews cells within the bone marrow to screen for lymphoma and other forms of cancer.

• ACTH stimulation test: This blood test screens for hypoadrenocorticism.

• Fungal serology or culture: Tests used to determine if fungal infections are present.

• Bacterial culture: Used to check for bacterial infections.

• Vitamin D assay: A test used to determine if vitamin D toxicity is suspected.

Determining the cause for hypercalcemia can be costly, due to the number of diagnostic tests that may be needed. Sometimes the cause is never found, which leads to a diagnosis of idiopathic hypercalcemia.

Treatment of Hypercalcemia in Cats

Treatment for hypercalcemia depends upon the underlying cause. If a cause can be found and treated, then this should help to prevent future bouts of hypercalcemia. Also, cats showing signs of hypercalcemia and/or have a high calcium level require treatment to lower it.  

Treatment may involve:

• Fluid therapy: Intravenous fluids are needed to correct any dehydration, which is an important step because dehydration can worsen hypercalcemia. IV fluids are also helpful to clear the kidneys of excess calcium by excreting it into the urine. 

• Diuretic medication: Furosemide may be needed to prevent the kidneys from reabsorbing calcium. It is crucial that the cat is always hydrated and has access to water. Without access to water, furosemide can cause a cat to become dehydrated.

• Steroid: Prednisolone reduces the ability for bone and the intestines to absorb calcium and helps the kidneys to excrete excess calcium into the urine. By doing so, this medication lowers the amount of calcium in the bloodstream.  

• Alendronate: This is an oral medication that is often prescribed when a cat is diagnosed with idiopathic hypercalcemia. Alendronate reduces bone resorption of calcium and helps to slow down bone loss.

• Diet: A change in diet may be indicated for cats with idiopathic hypercalcemia. A canned diet should be given instead of a dry cat formula to promote hydration. There are prescription canned diets to choose from that have helped with decreasing calcium levels (GI and renal diets) or minimizing the risk for calcium oxalate bladder stones (urinary diets), such as:

  • High-fiber gastrointestinal diet (Royal Canin Gastrointestinal Fiber Response, Purina OM, or Hill’s w/d)

  • Renal diet (Royal Canin Renal diets, Purina NF, or Hill’s k/d)

  • Urinary diet (Royal Canin Urinary SO, Purina UR, Hill’s c/d)

Recovery and Management of Hypercalcemia in Cats

After treatment has begun, your veterinarian will perform bloodwork to monitor the calcium level and determine the next steps of treatment. A cat that has previously had hypercalcemia can develop this condition again if the underlying cause is not identified and treated properly, or if treatment is not given as directed.

Most causes of hypercalcemia develop out of our control and cannot be prevented. The key is to keep your cat hydrated and bring your cat to your local veterinarian for a physical exam and bloodwork (which includes a calcium level check) every 6-12 months to allow for early detection.