🧬 Hypercalcemia in Dogs and Cats – A 2025 Vet’s Guide to Diagnosis and Treatment

By Dr Duncan Houston, BVSc

📊 What Is Hypercalcemia?

Hypercalcemia refers to abnormally high levels of calcium in the blood. Calcium is vital for many functions: bone health, muscle contractions, heart rhythm, and cellular signaling. But too much of it can become toxic, especially for organs like the kidneys. 🩺

⚖️ Types of Calcium in the Body

• Ionized Calcium: The active form (about 50% of total). Most important clinically.
• Bound Calcium: Attached to proteins like albumin (about 40%).
• Total Calcium: The sum of ionized + bound. This is what’s usually measured on lab panels.

🔁 How the Body Regulates Calcium

Calcium balance is tightly controlled by two hormones:

• Parathyroid Hormone (PTH) – Increases blood calcium by pulling it from bone and preventing its excretion via urine
• Calcitriol (Vitamin D) – Enhances calcium absorption from the gut, boosts release from bone, and reduces loss via the kidneys

Together, these hormones maintain calcium within a healthy range. But when disrupted, serious health issues can arise. ⚠️

❗ Why High Calcium Levels Are Dangerous

When calcium rises excessively, it leads to:

• 🦴 Bone softening and fractures
• 🧃 Increased urination and thirst
• 🚫 Kidney failure due to calcium crystal damage
• ⚙️ Mineralization of soft tissues

🧪 Common Causes of Hypercalcemia in Pets

• Lymphoma (most common in dogs)
• Parathyroid tumors
• Kidney failure
• Addison’s disease (hypoadrenocorticism)
• Vitamin D toxicity (rat poison, certain plants)
• Fungal infections
• Idiopathic hypercalcemia (most common cause in cats)

🔍 Step-by-Step Diagnostic Process

STEP 1: Check Ionized Calcium

Total calcium can be elevated due to dehydration or pH imbalance, but if ionized calcium is normal, the pet is not truly hypercalcemic.

STEP 2: Physical Exam

Check for:

• 🧠 Parathyroid growths (neck/throat)
• 🔍 Lymph node swelling
• 🍑 Anal gland tumors
• 🩺 Mammary tumors

STEP 3: Screen for Addison’s Disease

• Cortisol > 2.5 mg/dL → Addison’s ruled out
• Cortisol < 2.5 mg/dL → ACTH stimulation test needed

STEP 4: PTH and PTH-rP Blood Tests

Helps distinguish between:

STEP 5: Tumor Search

If cancer is suspected but not yet found:

• 📸 X-rays of chest and abdomen
• 🧬 Abdominal ultrasound
• 🔍 Bone marrow biopsy (for multiple myeloma)
• 🧪 Protein electrophoresis (if myeloma suspected)

📉 Emergency Levels

• 🐶 Calcium > 18 mg/dL = Medical Emergency
• ⚠️ >15 mg/dL requires prompt treatment

💊 Treatment Options for Hypercalcemia

1. 🥗 Diet

• Low-calcium diets (kidney support or stone prevention formulas)
• High-fiber additions (somewhat helpful)
• Light salt to promote calcium excretion (under vet guidance)

2. 💉 Bisphosphonates

• Inhibit osteoclasts to prevent calcium release from bones
• Alendronate (oral) or Zoledronate (IV)

3. 💊 Prednisolone (with caution)

Only use after cancer testing is done, especially to avoid masking lymphoma. Prednisolone helps reduce calcium by promoting renal excretion. ⛔ Not for use before full workup.

4. 💧 Saline Diuresis (IV Fluids)

• Used in hospital to support kidneys
• Flushes out calcium through urine

5. 💊 Furosemide (Lasix)

A diuretic that promotes calcium excretion—must be combined with IV fluids to avoid dehydration. 💧

📲 Ask A Vet for Calcium Monitoring and Support

Hypercalcemia can be tricky to diagnose and manage, but prompt action is crucial. Whether your pet's high calcium levels are mild or urgent, the Ask A Vet App gives you access to expert support every step of the way. 🐕📱

Visit AskAVet.com or open the app to consult with a veterinary professional 24/7. 🩺

✅ Summary: Key Takeaways

• 🧪 Always confirm with ionized calcium
• 🔍 Rule out cancer, kidney disease, or Addison’s
• ⚙️ Run PTH and PTH-rP tests for diagnosis
• 📉 Treat promptly if calcium > 15 mg/dL
• 💊 Use bisphosphonates, fluids, diet as needed

💬 Final Words from Dr Duncan Houston

High calcium isn’t just a lab value—it’s a signal something serious may be happening. With the right diagnostics and timely treatment, your pet can recover and thrive. 🐶🐱💚

Have questions or concerns about your pet’s blood work? Chat directly with a vet through the Ask A Vet App or visit AskAVet.com. We’re here to help. 🐾