Idiopathic Hypercalcemia in Cats: Expert Vet Insights 2025 🐱

Written by Dr Duncan Houston BVSc, professional veterinarian and founder of Ask A Vet.

In this comprehensive guide, we'll explore idiopathic hypercalcemia in cats—a condition where elevated calcium levels have no identifiable cause. We'll cover:

• ✅ What is hypercalcemia?
• ✅ Why calcium is vital
• ✅ Causes (with focus on idiopathic cases)
• ✅ Signs & symptoms in cats
• ✅ Diagnostic steps & key lab tests
• ✅ Treatment strategies
• ✅ Diet, lifestyle & long-term management
• ✅ When to seek vet help—or Ask A Vet

🔍 What Is Hypercalcemia?

Hypercalcemia is a condition where blood calcium exceeds normal levels. While calcium supports bone strength, muscle contraction, nerve transmission, and heart rhythm, too much can harm soft tissues and organs.

Calcium’s Role

Calcium is essential for:

• Strong bones & teeth
• Muscle function (including the heart)
• Nerve signaling
• Blood clotting

Why High Calcium Is Dangerous

Excess calcium may cause:

• Weakness, lethargy, tremors, even seizures
• Appetite loss, vomiting, constipation
• Increased thirst and urination, possible urinary stones
• Kidney damage
• Irregular heartbeat

🌐 Why “Idiopathic” Hypercalcemia?

“Idiopathic” means the cause remains unknown after extensive testing. In cats, this is one of the most common hypercalcemia types—as a diagnosis of exclusion.

Common underlying causes include:

• Chronic kidney failure
• Primary hyperparathyroidism
• Cancer (e.g., lymphoma, squamous cell carcinoma)
• Vitamin D toxins (plants, supplements, poison)
• Granulomatous diseases (fungal, protozoal)
• Rodenticides, topical Vitamin D creams

If all are ruled out—with normal kidney, PTH, PTH-rP, vitamin D, imaging exams—then idiopathic hypercalcemia is diagnosed.

🐾 Clinical Signs in Cats

Many cats with mild elevations show no symptoms. But when symptoms appear, they include:

• Lethargy, muscle weakness or tremors
• Poor appetite, vomiting, constipation
• Increased thirst and urination
• Straining to urinate if stones form

🧪 Diagnosis: A Thorough Process

Idiopathic hypercalcemia is confirmed only after comprehensive testing:

1. Confirm Elevated Calcium

Start with total calcium. To verify, test ionized calcium (iCa), the biologically active form—you must use anaerobic collection and proper handling.

2. Blood Chemistry & CBC

Assess kidney function (BUN, creatinine), phosphorus, albumin, liver enzymes, and total calcium. Anemia or inflammation may suggest cancer or kidney issues.

3. Hormone Tests: PTH and PTH‑rP

• PTH: high PTH + high iCa = primary hyperparathyroidism (rare in cats).
• Normal/low PTH + high iCa = parathyroid‑independent causes (like idiopathic or cancer).
• PTH-rP: high levels suggest humoral hypercalcemia of malignancy.

4. Imaging & Additional Tests

• Neck ultrasound (check parathyroids)
• X-rays or abdominal ultrasound (look for tumors, stones, organ damage)
• Retroviral testing (FeLV/FIV) due to association with lymphoma
• Vitamin D level if suspect overdose or toxicity

5. Diagnosis of Exclusion

If all results are normal—kidney, hormone, imaging, toxicity—then idiopathic hypercalcemia is diagnosed.

🩺 Treatment Options

Treatment depends on symptom severity; asymptomatic cats may be monitored, but others need intervention.

1. Medical Management

• IV fluids (saline): flushes out excess calcium.
• Furosemide: a mild diuretic to promote calciuresis.
• Prednisolone: slows calcium absorption.
• Bisphosphonates: reduce bone calcium release (used if chronic).

2. Dietary Management

A prescription diet low in calcium and Vitamin D, with proper calcium-phosphorus balance, is key. Ask your vet for brands like those from Woopf and Purrz that support feline health. Wet-food diets help reduce stone formation.

3. Home & Lifestyle Adjustments

• Ensure constant fresh water availability.
• Frequent urine monitoring to detect crystals or stones.
• Regular vet check-ups and blood tests.
• Engage with Ask A Vet for guidance between appointments.

4. Follow-Up & Monitoring

Retest total and ionized calcium every 4–8 weeks after treatment starts, then every 3–6 months. Monitor kidney function and phosphorus too.

📈 Prognosis & Management

• Cats with idiopathic hypercalcemia can live long, healthy lives with management.
• Complication risks include urinary stones and kidney damage.
• Prompt detection and consistent management improve outcomes.

🧡 Role of Ask A Vet, Woopf & Purrz

At Ask A Vet, we offer 24/7 telehealth check-ins to help you understand blood results ✅ and guide dietary adjustments. Brands Woopf and Purrz offer vet-formulated wet-food options ideal for managing urinary health and supporting calcium balance.

📌 Key Takeaways

• Test both total and ionized calcium to confirm diagnosis
• Use hormone testing + imaging to rule out all other causes
• Medical and dietary management can stabilize levels
• Regular monitoring is essential
• Vet partnership + Ask A Vet support helps maintain health

Need help interpreting your cat’s calcium results or building a diet plan? Reach out via Ask A Vet or talk to your primary veterinarian. Early attention ensures your cat stays comfortable and healthy 😊.

For additional support and personalized guidance, visit AskAVet.com and download the Ask A Vet app today!