Understanding Hypercalcemia in Dogs: Causes and Implications
Hypercalcemia in dogs refers to an elevated level of calcium in the blood. While calcium plays several crucial roles in the body—including muscle function, nerve signaling, blood clotting, and bone health—an excessive amount can lead to serious health issues. Typically, dogs present with serum calcium levels above 11.5 mg/dL, and it’s essential that pet owners and veterinarians understand the causes and potential consequences of this condition.
Calcium Regulation in the Canine Body
Calcium in the bloodstream exists in three forms:
- Ionized (free) calcium – biologically active and responsible for physiological functions
- Protein-bound calcium – primarily bound to albumin
- Complexed calcium – bound to phosphate, citrate, and lactate
The regulation of calcium is tightly controlled by three major hormones:
- Parathyroid Hormone (PTH) – increases calcium levels through bone resorption, renal reabsorption, and enhancing intestinal uptake via vitamin D activation
- Vitamin D – facilitates intestinal calcium absorption
- Calcitonin – lowers calcium levels by reducing bone resorption
Common Symptoms of Hypercalcemia
Clinical signs of elevated calcium in dogs can be subtle or severe, including:
- Increased thirst and urination (polyuria/polydipsia)
- Vomiting and constipation
- Lethargy and weakness
- Muscle twitching
- Loss of appetite and weight loss
- Arrhythmias or seizures in serious cases
Chronic hypercalcemia can result in kidney damage, stone formation, and soft tissue mineralization if not treated promptly.
Top Causes of Hypercalcemia in Dogs
The causes of high blood calcium in dogs are varied. Notably, the most common cause is malignancy-induced hypercalcemia. Below are the key contributors:
- Malignancy – Tumors such as lymphoma and anal sac adenocarcinoma frequently secrete PTH-related protein (PTHrP), which mimics the action of PTH. This leads to increased calcium levels.
- Primary Hyperparathyroidism – Often due to a benign tumor (adenoma) of the parathyroid gland, causing unregulated secretion of PTH.
- Kidney Disease – Both acute and chronic renal conditions can alter calcium and phosphorus levels due to impaired filtration and retention.
- Hypoadrenocorticism (Addison’s Disease) – A hormonal imbalance that increases calcium reabsorption in the kidneys.
- Vitamin D Toxicity – Ingestion of rodenticides or excessive supplements can allow increased GI absorption of calcium.
- Granulomatous Diseases – Conditions like fungal infections may prompt macrophages to produce calcitriol, leading to increased calcium.
- Osteolytic Disease – Bone tumors or infections can cause release of calcium into the bloodstream.
- Idiopathic Hypercalcemia – More common in cats, rare in dogs, and diagnosed after ruling out other causes.
- Spurious Causes – Lab errors, dehydration, or lipemia may falsely elevate test results.
Diagnosing Hypercalcemia
A multi-step approach is essential for accurate diagnosis:
- Confirm elevation with total and ionized calcium levels
- Repeat tests in fasted, well-hydrated dogs to rule out artifacts
- Run complete bloodwork and urinalysis
- Perform imaging (X-rays, ultrasound) and clinical exams
- Measure hormone levels like PTH and PTHrP
Key indicators help guide diagnosis:
- Normal or elevated PTH suggests primary hyperparathyroidism
- High PTHrP indicates malignancy-induced hypercalcemia
- Vitamin D metabolites aid in identifying toxicity
Treatment Strategies
The course of treatment depends on the underlying cause:
- IV fluid therapy to increase excretion of calcium through the kidneys
- Furosemide enhances calcium loss in urine post-rehydration
- Glucocorticoids suppress calcium absorption, but should be delayed until diagnosis to prevent masking disease
- Bisphosphonates inhibit bone breakdown in malignancy cases
- Dietary management may benefit chronic or idiopathic cases
Prognosis and Monitoring
Outcome varies based on the root cause:
- Dogs with Addison’s disease or treatable tumors often respond well
- Malignant-related hypercalcemia has a guarded prognosis, especially if aggressive or metastatic
Monitoring is essential during and after treatment to track calcium levels and clinical progress.
Conclusion
Hypercalcemia is frequently a sign of a significant underlying disease in dogs. Because cancer is the most common cause, identifying the source and initiating prompt, targeted therapy is crucial. Routine bloodwork, early veterinary intervention, and informed pet care can drastically improve outcomes.
