Hypercalcemia — elevated blood calcium — is a serious finding in cats that most often signals lymphoma, chronic kidney disease, or idiopathic disease. It causes increased thirst, lethargy, vomiting, and, if untreated, kidney failure. Early blood testing is the only way to detect it before organ damage sets in.
Last reviewed: June 2026
What Is Hypercalcemia in Cats?
Hypercalcemia means the total calcium concentration in the blood exceeds the normal range (roughly 8.5–10.5 mg/dL in cats). Mild elevations may cause few noticeable signs; severe or prolonged elevations cause calcium to deposit in soft tissues, particularly the kidneys, where it triggers irreversible tubular damage. As described in Nelson & Couto's Small Animal Internal Medicine, the most common causes in cats are idiopathic hypercalcemia (the most frequent overall), lymphoma, chronic kidney disease, and primary hyperparathyroidism — in contrast to dogs, where neoplasia is more dominant. Roughly 30–40% of feline hypercalcemia cases are idiopathic, meaning no underlying disease is identified despite complete workup.
Signs of Hypercalcemia in Cats
Early signs are nonspecific and often attributed to other causes:
- Excessive thirst and urination (PU/PD) — calcium interferes with renal concentrating ability
- Lethargy and weakness — elevated calcium impairs neuromuscular function
- Reduced appetite or vomiting — gastrointestinal effect of high calcium
- Constipation — smooth muscle hypomotility
- Weight loss — especially if lymphoma is the underlying cause
- Muscle twitching or stiff gait — in very high calcium states
The IRIS CKD Staging Guidelines, 2023 note that hypercalcemia and CKD are bidirectionally linked in cats — CKD can cause calcium dysregulation, and hypercalcemia accelerates CKD progression, making early detection critical.
Common Causes
| Cause | Notes |
|---|---|
| Idiopathic hypercalcemia | Dietary calcium excess or aberrant intestinal absorption; responds to low-calcium diet |
| Lymphoma | Most common neoplastic cause; ionized calcium often markedly elevated |
| Chronic kidney disease | CKD-mineral-bone disorder; calcium-phosphorus dysregulation |
| Primary hyperparathyroidism | Parathyroid adenoma; solitary nodule on cervical ultrasound |
| Hypervitaminosis D | Excessive vitamin D supplementation or rodenticide (cholecalciferol bait) toxicity |
| Granulomatous disease | Rare; FIP, histoplasmosis |
Diagnosis and Costs
Diagnosis requires measuring ionized calcium (more accurate than total calcium) alongside a full chemistry panel and urinalysis. Initial bloodwork costs $100–250. If lymphoma is suspected, chest radiographs ($150–300) and abdominal ultrasound ($300–500) are standard. Fine-needle aspiration of enlarged lymph nodes adds $100–200. Parathyroid ultrasound requires a specialist.
The AAFP-AAHA Feline Life Stage Guidelines, 2021 recommend annual chemistry panels in senior cats (≥7 years) specifically to catch hypercalcemia and kidney disease before clinical signs develop.
Treatment
Treatment targets the underlying cause:
- Idiopathic: high-fiber, low-calcium diet (avoid diets with added calcium); often resolves calcium within weeks
- Lymphoma: chemotherapy (CHOP protocol or prednisolone-based single-agent); costs $2,000–6,000+ for multi-agent protocols
- Primary hyperparathyroidism: surgical parathyroidectomy or ultrasound-guided ablation; cost $1,500–3,500
- Vitamin D toxicity: IV fluids, furosemide, corticosteroids, bisphosphonates — hospitalization $500–1,500+
- Supportive: IV saline diuresis to lower calcium acutely when levels are dangerously high
When to See a Vet
Call your vet today if:
- Your cat is drinking noticeably more water than usual
- Lethargy has persisted for more than two days
- Your cat is vomiting repeatedly or not eating
- Your older cat hasn't had a blood panel in more than a year
Go to the ER immediately if:
- Your cat is extremely weak, cannot stand, or is having muscle tremors
- You suspect vitamin D rodenticide ingestion (cholecalciferol bait)
- Your cat has collapsed
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Frequently Asked Questions
How is hypercalcemia in cats diagnosed? A routine blood panel can detect elevated total calcium, but ionized calcium measurement is more reliable. Once confirmed, follow-up testing (urinalysis, chest X-ray, abdominal ultrasound, lymph node aspirate) identifies the underlying cause. Initial workup costs $200–600 depending on how extensive the investigation is.
Can hypercalcemia kill a cat? Yes, if untreated. Chronically elevated calcium deposits in the kidney tubules causing progressive, irreversible renal failure. Extremely high levels (above 14–15 mg/dL) can cause cardiac arrhythmias and neurological crises. Early detection and treatment prevent these outcomes.
Is hypercalcemia in cats always cancer? No — idiopathic hypercalcemia is the most common cause in cats and has no identified malignancy. However, lymphoma must be ruled out because it can look identical on bloodwork alone. A thorough workup (ultrasound, aspirates) is needed to distinguish them.
What diet helps cats with hypercalcemia? For idiopathic cases, a high-fiber, low-calcium prescription diet (such as those formulated for urinary health or kidney support) typically reduces calcium levels within 4–8 weeks. Avoid cottage cheese, high-calcium treats, and raw diets with unbalanced bone content. Dietary change alone should always be confirmed with rechecking bloodwork.
What does hypercalcemia treatment cost in cats? Initial diagnostics: $200–600. Dietary management: $60–120/month for prescription food. Lymphoma chemotherapy: $2,000–6,000+ for multi-drug protocols. Parathyroid surgery: $1,500–3,500. IV crisis management: $500–1,500+ hospitalization. Catching it early via routine annual bloodwork is far less expensive than treating organ failure.
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