Understanding the Causes of High Calcium in Dogs
When your dog has high blood calcium levels—a condition called hypercalcemia—it signals that something significant is happening inside their body. Calcium is crucial for muscle movement, nerve function, blood clotting, and building strong bones. But when those levels rise above normal (over about 11.5 mg/dL), it can lead to serious health problems.
How the Body Regulates Calcium
The body keeps calcium in a tight balance using several hormones. The parathyroid glands release parathyroid hormone (PTH) if calcium drops too low. PTH pulls calcium from bones, helps the kidneys retain it, and boosts absorption from food by activating vitamin D. On the flip side, calcitonin helps lower calcium but plays a smaller role day-to-day.
Main Causes of Hypercalcemia in Dogs
If your dog’s calcium is high, here are the most common reasons:
- Cancer (Malignancy): The number one cause is certain cancers—especially lymphoma and anal sac adenocarcinoma. These tumors can make substances mimicking PTH (called PTHrP), tricking the body into raising blood calcium.
- Primary Hyperparathyroidism: A growth (usually benign) on the parathyroid gland can make it produce too much PTH, regardless of actual calcium needs.
- Kidney Disease: Both acute and chronic kidney problems disrupt how the body handles minerals like calcium and phosphorus. Damaged kidneys may not excrete enough calcium.
- Addison’s Disease (Hypoadrenocorticism): With this adrenal disorder, low hormone levels cause the body to retain more calcium.
- Vitamin D Toxicity: Dogs may ingest rodenticides, human supplements, certain plants, or get overdosed on vitamin D. Too much vitamin D dramatically raises blood calcium.
- Granulomatous Diseases: Some infections—especially fungal ones like blastomycosis or histoplasmosis—cause immune cells to produce extra calcitriol (active vitamin D).
- Osteolytic Disease: Bone tumors or severe bone infections break down bone tissue and release stored calcium into the bloodstream.
- Spurious Causes: Sometimes lab errors or dehydration falsely elevate test results. Always confirm with repeat testing under proper conditions.
- Idiopathic Hypercalcemia: Rare in dogs but more common in cats; this diagnosis is made only after ruling out all other causes.
The Diagnostic Process
Your vet will start by confirming true hypercalcemia—preferably by measuring ionized, not just total, calcium since dehydration or high protein can skew results. If confirmed, they’ll perform a thorough physical exam: checking lymph nodes for swelling (suggesting lymphoma), feeling for anal sac masses, and examining the neck for parathyroid enlargement.
The workup usually includes:
- Bloodwork and urinalysis
- X-rays or ultrasound imaging
- PTH and PTHrP measurement: High PTH with high calcium points to parathyroid disease; high PTHrP suggests cancer.
- Kidney function tests
- If vitamin D toxicity is suspected, special blood tests for vitamin D metabolites may be done.
Symptoms of High Calcium in Dogs
The signs are often vague at first but can become serious if untreated. Watch for:
- Lethargy or weakness
- Poor appetite or vomiting
- Increased thirst and urination (polyuria/polydipsia)
- Constipation or weight loss
- Twitching muscles or even seizures in severe cases
- If prolonged: kidney damage, bladder/kidney stones, mineral deposits in organs
Treatment Approaches
Treatment depends on what’s causing the problem. For life-threatening hypercalcemia, your vet will act quickly to lower levels while searching for an underlying cause. Common steps include:
- IV fluids (0.9% sodium chloride): Hydration helps flush out excess calcium via the kidneys.
- Furosemide (loop diuretic): Used after rehydration to further promote urinary loss of calcium—but must be used carefully to avoid dehydration.
- Steroids (glucocorticoids): These reduce bone breakdown and intestinal absorption of calcium but are avoided until a diagnosis is confirmed because they can mask some cancers like lymphoma.
- Bisphosphonates: Drugs like pamidronate inhibit bone resorption; especially useful for cancer-related cases.
- Surgery or specific therapy: For example, removing a parathyroid tumor or treating Addison’s disease with hormone replacement.
Your vet may also recommend dietary changes or less common medications depending on your dog’s unique situation.
The Importance of Identifying the Cause Early
You don’t want to ignore high blood calcium—it almost always means there’s an underlying medical issue that needs attention. Some causes respond well to treatment; others carry a guarded outlook if aggressive cancer is present. Untreated hypercalcemia can permanently damage organs like the kidneys and heart.
