High Calcium in Cats: Normal Range, Causes & What the Chemistry Panel Value Means
Last reviewed: April 2026
Calcium on your cat's chemistry panel is one of the most important values to understand when it's abnormal. The normal range is 8.8–11.0 mg/dL (total) or 1.12–1.40 mmol/L (ionized). High calcium has multiple possible causes — and in cats, the most common one is not cancer. Low calcium causes muscle tremors and tetany. Here's how to interpret every level.
Quick Reference
Idiopathic, HPT, lymphoma, vitamin D
Hypoparathyroidism, eclampsia, Fleet enemas
Total Calcium vs. Ionized Calcium — Why the Distinction Matters
The number on a standard chemistry panel is total calcium — the sum of three fractions:
| Fraction | % of Total | Biologically Active? | Affected By |
|---|---|---|---|
| Protein-bound (mainly albumin) | ~45% | No | Albumin level, pH |
| Complexed (citrate, phosphate) | ~10% | No | Phosphorus, pH |
| Ionized (free calcium) | ~45% | Yes — the active fraction | PTH, vitamin D, pH |
Always Confirm Abnormal Total Calcium with Ionized Calcium
For cats specifically, measuring ionized calcium alongside PTH is essential for diagnosis — particularly because idiopathic hypercalcemia (suppressed PTH with elevated ionized calcium) and primary hyperparathyroidism (elevated PTH with elevated ionized calcium) look identical on a routine chemistry panel but require completely different treatment.
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High Calcium — Severity Tiers
Causes of High Calcium in Cats
A helpful framework: look at ionized calcium + PTH together. These two values narrow the differential dramatically.
| Ionized Ca | PTH | Likely Diagnosis |
|---|---|---|
| High | High or inappropriately normal | Primary hyperparathyroidism (parathyroid adenoma) |
| High | Low (suppressed) | Idiopathic hypercalcemia, cancer (PTHrP), vitamin D toxicity |
| Normal or low | High | Renal secondary hyperparathyroidism (CKD) |
| Low | Low or undetectable | Hypoparathyroidism |
1. Idiopathic Hypercalcemia (IHC) — Most Common in Cats
Idiopathic hypercalcemia is a feline-specific condition with no equivalent in dogs. Ionized calcium is persistently elevated, but PTH is suppressed (low) — the parathyroid glands are responding correctly by shutting down PTH production, which is actually what should happen when calcium is high. The problem is that the source of calcium elevation is upstream and unknown.
- Middle-aged to older cats most affected; no strong breed predisposition
- Associated with calcium oxalate urinary stones and chronic constipation
- Theories: excess intestinal calcium absorption, altered bone calcium turnover, dietary triggers
- PTHrP is negative (no cancer signal)
Treatment options: dietary change (high-fiber, low-oxalate, or hydrolyzed protein diet), prednisolone (reduces intestinal calcium absorption), and alendronate (bisphosphonate — reduces bone resorption) for refractory cases.
See the full hyperparathyroidism in cats post for a detailed workup and treatment guide for IHC.
2. Primary Hyperparathyroidism (Parathyroid Adenoma)
A benign tumor of the parathyroid gland secretes PTH autonomously — ignoring normal feedback regulation. PTH is high (or inappropriately normal despite high calcium), ionized calcium is high, and phosphorus is low (PTH tells kidneys to waste phosphorus). The parathyroid adenoma is usually found on ultrasound as a small nodule near the thyroid.
Surgery (parathyroidectomy) is curative in most cats, but post-operative hypocalcemia is the main complication — the remaining parathyroid glands have been suppressed for months and take time to recover. Close post-surgical monitoring and calcium supplementation are required.
3. Cancer (Humoral Hypercalcemia of Malignancy)
Tumors — most commonly lymphoma in cats — secrete PTH-related protein (PTHrP), which mimics PTH and raises blood calcium. Unlike true PTH, PTHrP is not detected by standard PTH assays and requires separate testing.
Cancers That Cause Hypercalcemia in Cats
- Lymphoma: Most common cancer cause — mediastinal lymphoma particularly likely
- Squamous cell carcinoma: Oral SCC can produce PTHrP
- Multiple myeloma: Plasma cell tumor; also causes high protein and bone lesions
- Other carcinomas: Various solid tumors can produce PTHrP
Pattern: ionized calcium elevated, PTH suppressed (low), PTHrP elevated. Chest x-rays and abdominal ultrasound are key — mediastinal masses (cranial chest, pushing the trachea upward on x-ray) are classic for mediastinal lymphoma.
4. Vitamin D Toxicity
Excess vitamin D causes unregulated intestinal calcium absorption and bone resorption, driving calcium to dangerous levels. Sources in cats include:
- Vitamin D supplements: Accidental overdose or supplemented pet foods with formulation errors
- Cholecalciferol-based rodenticides: Exposure through eating a poisoned rodent (relay toxicity) or direct ingestion
- Calcipotriene (Dovonex): A human psoriasis cream containing a vitamin D analogue — cats that groom owners who applied this cream can ingest a toxic dose
- Certain plants: Jasmine (day-blooming), some Solanum species
Vitamin D Toxicity Is a Veterinary Emergency
5. Granulomatous Disease
Inflammatory granulomas (clusters of macrophages) can produce calcitriol (active vitamin D) independently of kidney regulation — raising calcium from within the granuloma. In cats this occurs most commonly with fungal disease (histoplasmosis, cryptococcosis) and occasionally with FIP. PTH is suppressed; 1,25-dihydroxyvitamin D (calcitriol) is elevated if measured. Treating the underlying infection resolves the hypercalcemia.
6. Renal Secondary Hyperparathyroidism (CKD)
In CKD, impaired phosphorus excretion and reduced calcitriol production drive PTH upward. Calcium is usually normal or low-normal in renal secondary HPT — the elevated PTH is trying to pull calcium up from bone but cannot compensate fully. Occasionally, total calcium appears slightly elevated in CKD cats. The pattern (high PTH, high phosphorus, high BUN/creatinine/SDMA, and normal or mildly elevated calcium) points to CKD rather than primary hyperparathyroidism.
Low Calcium (Hypocalcemia) in Cats
Low calcium is less common than high calcium in cats but is more immediately dangerous when severe — it causes uncontrolled muscle activity ranging from tremors to life-threatening tetany and seizures.
Clinical Signs of Hypocalcemia
- • Muscle tremors or fasciculations (fine twitching)
- • Facial rubbing or pawing at face
- • Stiff or stilted gait
- • Tetany (rigid muscle contractions)
- • Seizures in severe cases
- • Hypersensitivity to touch or sound (hyperesthesia)
- • In chronic hypocalcemia: cataracts (calcium deposits in the lens)
1. Hypoparathyroidism — Most Common Cause
Without PTH, the kidneys cannot retain calcium and bones do not release it — blood calcium falls. In cats, the most common cause is accidental damage or removal of the parathyroid glands during thyroidectomy for hyperthyroidism. The parathyroid glands sit embedded in or adjacent to the thyroid and can be inadvertently removed or devascularized during surgery.
- Signs appear 1–5 days after thyroidectomy as calcium gradually falls
- Post-surgical monitoring of calcium is standard practice after thyroidectomy
- Treatment: IV calcium gluconate acutely; calcitriol (active vitamin D) + oral calcium long-term
- Some cats recover parathyroid function over weeks to months; others require lifelong supplementation
Primary immune-mediated hypoparathyroidism (without surgery) is rare in cats.
2. Eclampsia (Puerperal Tetany) in Nursing Queens
A nursing queen with a large litter loses calcium rapidly into her milk — faster than she can absorb it from her diet. Blood calcium drops suddenly, causing the muscle signs of hypocalcemia. Eclampsia typically occurs in the first 1–3 weeks of nursing.
Eclampsia in Nursing Cats Is an Emergency
3. Phosphate Enema Toxicity (Fleet Enemas)
Fleet enemas and other sodium phosphate enemas are extremely dangerous in cats. Cats rapidly absorb the phosphate through the colonic mucosa, causing a sudden massive spike in blood phosphorus. High phosphorus binds calcium, driving it precipitously low. The combination of hyperphosphatemia, hypocalcemia, and the sodium load can be fatal within hours.
Never Give Fleet Enemas to Cats
4. Other Causes
- Ethylene glycol (antifreeze) toxicity: Causes calcium oxalate crystal formation, trapping calcium — while also causing severe acute kidney failure
- Acute pancreatitis: Calcium is consumed by saponification of fat (calcium soap) in areas of pancreatic fat necrosis
- Hypoalbuminemia (pseudohypocalcemia): Low albumin causes total calcium to appear low — but ionized calcium is normal, and the cat has no hypocalcemic symptoms. Confirm with ionized calcium before treating
- Hypomagnesemia: Magnesium is needed for PTH secretion and response; severe magnesium deficiency can cause hypocalcemia that does not respond to calcium supplementation until magnesium is corrected
Chemistry Panel Pattern Recognition
Pattern 1: High total Ca, normal ionized Ca, low albumin
Artifact — albumin is concentrating the total calcium reading. True calcium status is normal. No treatment needed for calcium; address the cause of low albumin.
Pattern 2: High ionized Ca + suppressed PTH + negative PTHrP + middle-aged cat
Idiopathic hypercalcemia most likely. Dietary trial (high-fiber, hydrolyzed protein diet) is often first-line. If refractory, prednisolone or alendronate.
Pattern 3: High ionized Ca + suppressed PTH + elevated PTHrP
Cancer until proven otherwise. Chest x-ray (mediastinal mass?), abdominal ultrasound (lymph nodes?), bone marrow evaluation if lymphoma suspected. Urgent oncology workup.
Pattern 4: High ionized Ca + elevated or inappropriately normal PTH + low phosphorus
Primary hyperparathyroidism — parathyroid adenoma. Neck ultrasound to find the nodule. Parathyroidectomy or ethanol ablation.
Pattern 5: Normal or low ionized Ca + high PTH + high phosphorus + high BUN/creatinine
Renal secondary hyperparathyroidism from CKD. Manage CKD — phosphorus restriction, phosphate binders, calcitriol. Not a parathyroid surgery case.
Pattern 6: Low ionized Ca + low or absent PTH + post-thyroidectomy
Hypoparathyroidism from parathyroid damage during surgery. IV calcium gluconate acutely; calcitriol + oral calcium long-term.
Pattern 7: Extreme hypercalcemia + recent toxin exposure + no other explanation
Vitamin D toxicity (cholecalciferol, Dovonex, plant exposure). Emergency hospitalization, aggressive IV saline diuresis, bisphosphonate therapy, pamidronate if available.
Related Reading
Hyperparathyroidism in Cats
Deep dive into primary HPT, renal secondary HPT, and idiopathic hypercalcemia — the three feline forms.
High Calcium in Dogs
How calcium disorders differ in dogs — cancer most common cause, Addison's, vitamin D toxicity.
Cat Kidney Values Explained
BUN, creatinine, SDMA, phosphorus — how CKD drives calcium and PTH changes.
Cat Hyperthyroidism Symptoms & Blood Tests
Understanding T4 and why thyroidectomy carries a risk of post-surgical hypocalcemia.
This article is for educational purposes only and does not constitute veterinary medical advice. Always consult a licensed veterinarian for diagnosis and treatment decisions regarding your pet's health.