Cats Drinking Excessive Water — Causes of Hypercalcemia and When to Visit the Vet

EndocrineDiseasesMeongsiljang Veterinary Advisory Board

Feline hypercalcemia is an endocrine disorder characterized by elevated blood calcium levels, making early detection crucial. The main causes include cancer, kidney disease, and excessive calcium supplementation.

Feline Hypercalcemia is an Endocrine Disorder Characterized by Elevated Blood Calcium Levels

An anatomical image showing calcium deposits in a cat’s blood vessels and kidneys

Feline hypercalcemia is an endocrine disorder caused by elevated blood calcium levels exceeding the normal range, and early detection is key to effective treatment and management. - Blood calcium levels: Hypercalcemia is diagnosed when a cat’s total blood calcium exceeds 11 mg/dL or ionized calcium surpasses 1.4 mmol/L (5.6 mg/dL). Prolonged elevation can strain organs such as the kidneys. - Common causes: Malignant tumors, kidney damage, and idiopathic hypercalcemia are frequent causes, while primary hyperparathyroidism, hypoadrenocorticism (Addison’s disease), and vitamin D toxicity can also contribute. - Importance of early diagnosis: Mild hypercalcemia may present with few or no symptoms, making routine blood tests essential for timely detection. - Foundation of treatment: Accurately identifying the underlying cause is the first step toward effective treatment. - Preventive care: Careful dietary management and medication adherence under veterinary guidance are crucial.

Main Causes Include Cancer, Kidney Disease, and Excessive Supplement Use

The most common cause of hypercalcemia in cats is malignant tumors, which elevate blood calcium levels by secreting parathyroid hormone-related protein (PTHrP) or by locally resorbing bone. - Cancer-associated hypercalcemia: This is frequently seen in conditions such as lymphoma and squamous cell carcinoma, and calcium levels may rise if the cancer metastasizes to the bones. - Kidney damage: Kidney disease is one of the common causes of hypercalcemia in cats. - Endocrine and other causes: Primary hyperparathyroidism, hypoadrenocorticism (Addison’s disease), and vitamin D excess (from over-supplementation) can also be underlying causes. - Idiopathic cases: Idiopathic hypercalcemia, where no specific cause can be identified, is relatively common in cats, particularly affecting young to middle-aged individuals. - Importance of identifying the cause: It is essential to determine the underlying cause before initiating treatment to ensure effective management.

An image of a cat sitting next to a calcium supplement bottle, with a warning sign present.

Be Sure to Check for Key Symptoms and Signs

The symptoms of hypercalcemia in cats can vary, but they are generally nonspecific, and cats tend to show milder signs than dogs. In mild cases, there may be almost no noticeable symptoms. Common signs include decreased appetite, vomiting, constipation, and polyuria-polydipsia (increased water intake and urination). If the condition worsens, lethargy, muscle weakness, and heart rhythm abnormalities (arrhythmias) may occur. Since calcium deposition in the kidneys can lead to kidney damage, it’s a good idea to have your cat checked if any unusual symptoms persist.

Decreased appetite: A sudden drop in food intake.

Polyuria-polydipsia: Drinking more water and producing more urine.

Vomiting and constipation: Repeated vomiting or difficulty passing stool.

Lethargy: Staying in one place all day with little movement.

Muscle weakness: Difficulty walking or appearing weak and tired.

A lethargic cat lying on the floor, with its hind legs appearing weak.

Immediate Veterinary Visit Required for Severe Symptoms or Cardiac Arrhythmia

If your cat experiences severe vomiting, marked lethargy and weakness, or an irregular heartbeat (arrhythmia), seek veterinary care immediately. Hypercalcemia can alter the excitability of nerves and muscles, leading to cardiac arrhythmias, weakness, and lethargy. Because disturbances in heart rhythm can be life-threatening, prompt evaluation and treatment are essential. Immediate veterinary attention is crucial.

Diagnosis is Confirmed via Blood Tests and Imaging

Feline hypercalcemia is diagnosed when total blood calcium exceeds 11 mg/dL or ionized calcium surpasses 1.4 mmol/L (5.6 mg/dL) on blood tests. - Blood test criteria: In addition to calcium levels, we also evaluate phosphorus (P) and kidney function markers. Since total calcium can be influenced by sample conditions such as lipemia or hemolysis, measuring ionized calcium is often more helpful. - Tests to identify the cause: Imaging studies like X-rays and ultrasounds help check for tumors, calcium deposits in tissues, or stone formation. - Hormone tests: We measure levels of parathyroid hormone (PTH), PTH-related peptide (PTHrP), and vitamin D metabolites (calcidiol and calcitriol) to differentiate the underlying cause. - Importance of an accurate diagnosis: Treatment is difficult without knowing the cause, so a comprehensive evaluation is essential. - Screening recommendation: Since hypercalcemia can sometimes be discovered incidentally during blood tests even in asymptomatic cats, we recommend including blood work in regular health checkups.

A veterinarian drawing a blood sample from a cat, with laboratory equipment in the background.

Treatment Focuses on Eliminating the Underlying Cause and Regulating Calcium

Treatment depends on the underlying cause of hypercalcemia, with definitive therapy focused on identifying and treating the primary disease. If cancer is the cause, tumor removal or chemotherapy may be necessary. When high calcium levels result from conditions such as kidney dysfunction, fluid therapy is used to promote calcium excretion. In severe cases, diuretics, calcitonin, or glucocorticoids (steroids) may be administered to lower calcium levels; however, steroids should be used cautiously until a cancer diagnosis is confirmed. If excessive supplement intake is the cause, it should be stopped immediately and calcium intake restricted. Treatment requires not only short-term stabilization but also long-term management.

A veterinarian administering intravenous therapy to a cat, with monitoring equipment in place.

Home Care Must Be Meticulously Managed Under Veterinary Guidance

Regular blood tests and health check-ups are essential even after treatment. - Dietary Management: Avoid foods or supplements high in calcium, and follow the diet plan recommended by your veterinarian. - Hydration: Ensure your pet drinks plenty of water to support kidney function and promote calcium excretion. - Physical Activity: Regular play and exercise help prevent muscle weakness and provide emotional stability. - Medication Adherence: Failing to strictly follow medication instructions can cause calcium levels to rise again. - Routine and Stress Management: Reducing stress and maintaining a consistent daily routine can speed up recovery.

A cat drinking water from a clean bowl, with a natural light background.

Certain Breeds May Be More Susceptible to Hypercalcemia

It’s difficult to definitively say that hypercalcemia occurs more frequently in specific breeds. However, idiopathic hypercalcemia, where the cause is unknown, is relatively common in cats, primarily affecting young to middle-aged individuals. On the other hand, causes such as tumors are more prevalent in older cats, meaning the condition can occur at any age. Since symptoms may be subtle, early detection through regular health check-ups is crucial, and it’s advisable to develop a management plan in consultation with your veterinarian.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Is hypercalcemia in cats treatable?

With accurate diagnosis and appropriate treatment, recovery is often possible. The fundamental approach involves addressing the underlying condition, making early diagnosis crucial.

What foods should be avoided when hypercalcemia occurs?

To reduce calcium absorption in the gastrointestinal tract, it's best to limit high-calcium foods and supplements. Following a diet recommended by your veterinarian is the safest approach.

Is hypercalcemia common in cats?

This condition is not particularly rare, and in cats, common causes include malignant tumors, kidney damage, and idiopathic hypercalcemia. Because symptoms may be subtle, regular check-ups are important.

How do veterinarians treat hypercalcemia?

We check calcium levels through blood tests and proceed with treatments such as fluid therapy, medications (diuretics, calcitonin, steroids, etc.), or surgery, depending on the cause. Long-term management is necessary.

Does hypercalcemia cause pain in cats?

In severe cases, lethargy and muscle weakness may occur. If you notice reduced mobility or signs of low energy, it’s best to monitor your pet closely and schedule a veterinary check-up.

Comparison of Characteristics and Treatment Approaches by Cause of Hypercalcemia

Item	Main Features	Treatment Direction	Prognosis
Cancer-Related	Sharp rise in blood calcium, bone damage	Tumor removal, chemotherapy	Moderate to Poor
Kidney Disease	Impaired calcium excretion, polyuria and polydipsia	Fluid therapy, kidney protection	Moderate
Excessive Supplements	Levels recover after discontinuing supplements	Discontinue supplements, dietary management	Good
Idiopathic	Unknown cause, requires monitoring of the course	Focused on symptom management	Moderate to Good

The treatment success rate varies depending on early diagnosis and whether the cause is removed.

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References

[1] Chew DJ, Leonard M, Muir W. Effect of sodium bicarbonate infusions on ionized calcium and total calcium concentrations in serum of clinically normal cats. Am J Vet Res. 1989;50(1):145–150.

[2] Taylor SS, Sparkes AH, Briscoe K, et al. ISFM consensus guidelines on the diagnosis and management of hypertension in cats. J Feline Med Surg. 2017;19(3):28.

[3] Feline Emergency and Critical Care Medicine, 2nd Ed. Elsevier, 2017. Chapter 32: Hypercalcemia in Cats.