Hypercalcemia in Cats: Causes, Signs & Treatment

Hypercalcemia means there is too much calcium circulating in your cat's blood. Calcium is essential for nerve function, muscle contraction, blood clotting, and bone health, but levels need to stay within a narrow range. When they rise above normal, the kidneys, urinary tract, digestive system, heart, and nervous system can all be affected.

This condition is not one single disease. It is a finding on bloodwork that tells your vet something else may be going on. In some cats, the increase is mild and found during routine screening. In others, calcium rises enough to cause dehydration, constipation, urinary problems, weakness, or more serious complications.

One important detail is that ionized calcium is the most useful test for confirming true hypercalcemia. Total calcium can be misleading in some situations, so your vet may recommend repeat testing before deciding how serious the problem is.

The outlook depends less on the number alone and more on the underlying cause. A cat with mild idiopathic hypercalcemia may do well for a long time with monitoring and diet changes, while a cat with severe hypercalcemia from cancer or advanced kidney disease may need faster, more intensive care.

Hypercalcemia in cats has several possible causes, and the list matters because treatment depends on the reason calcium is high. Common causes include chronic kidney disease, idiopathic hypercalcemia (meaning no clear cause is found after a full workup), cancer, primary hyperparathyroidism, and hyperthyroidism. Less common causes include vitamin D toxicosis, calcium or vitamin A over-supplementation, granulomatous inflammatory disease, and some medications.

In cats, idiopathic hypercalcemia is especially important because it is one of the more common explanations when testing does not reveal cancer, parathyroid disease, or another obvious trigger. These cats may have constipation, urinary stones, or no signs at all. Chronic kidney disease is also a major contributor in feline patients and may overlap with dehydration, poor urine concentration, and other lab changes.

Cancer-related hypercalcemia can occur with conditions such as lymphoma, squamous cell carcinoma, or multiple myeloma. In these cases, the calcium problem is secondary to the cancer process. Primary hyperparathyroidism is less common in cats, but it can happen when a parathyroid tumor causes excess parathyroid hormone production.

Because the causes range from manageable chronic conditions to urgent systemic disease, it is important not to assume the answer from one abnormal lab value. Your vet will use your cat's history, exam findings, repeat calcium testing, urine results, and imaging to narrow the list.

Diagnosis starts with confirming that the calcium increase is real. Your vet may repeat the blood test, often after fasting, and may check ionized calcium, which is the biologically active form and the most accurate way to assess true calcium status. A complete blood count, chemistry panel, and urinalysis are usually part of the first step.

From there, the workup focuses on the cause. Your vet may recommend urine culture, blood pressure measurement, thyroid testing, and imaging such as abdominal radiographs or ultrasound to look for urinary stones, kidney changes, masses, or other clues. Chest radiographs may be helpful if cancer is a concern.

If the cause is still unclear, more targeted tests may be needed. These can include parathyroid hormone (PTH), parathyroid hormone-related protein (PTHrP), vitamin D testing, or cervical ultrasound to evaluate the parathyroid glands. Idiopathic hypercalcemia is usually diagnosed only after other causes have been ruled out.

This stepwise approach helps keep care practical. Some cats need only repeat testing and monitoring at first, while others need a broader workup right away because they are sick, dehydrated, or have signs that suggest stones, kidney disease, or cancer.

Not every case of hypercalcemia can be prevented, because some causes are linked to cancer, parathyroid disease, or idiopathic changes that are outside a pet parent's control. Still, early detection can make a real difference. Routine wellness exams and screening bloodwork are especially helpful for middle-aged and senior cats, since some cats with hypercalcemia look normal at home.

Avoid giving calcium, vitamin D, or other supplements unless your vet recommends them. Keep rodenticides, psoriasis creams containing vitamin D analogs, and other potential toxins out of reach. If your cat has chronic kidney disease, hyperthyroidism, constipation, or a history of urinary stones, follow-up care matters because these conditions can overlap with calcium problems.

Hydration also helps support urinary and kidney health. Encourage water intake in ways your cat likes, such as canned food, water fountains, or multiple clean bowls. That will not prevent every cause of hypercalcemia, but it can help reduce stress on the urinary tract.

The most practical prevention plan is regular monitoring. If your cat has had high calcium before, ask your vet how often to recheck bloodwork and urine. Catching a trend early may allow for more treatment options and fewer complications.