What is a common cause of hypercalcemia in veterinary patients?

Primary hyperparathyroidism and malignancy are significant causes of hypercalcemia in veterinary patients due to their direct effects on calcium homeostasis.

In primary hyperparathyroidism, an overproduction of parathyroid hormone (PTH) leads to increased calcium release from bones, enhanced intestinal absorption of calcium, and decreased renal excretion of calcium, resulting in elevated serum calcium levels. This condition is frequently seen in older pets and breeds predisposed to endocrine disorders.

Malignancies can cause hypercalcemia through several mechanisms, including paraneoplastic syndromes where tumors produce substances that mimic PTH (known as PTHrP), leading to increased calcium levels in the bloodstream. Common tumors in pets that lead to hypercalcemia include lymphoma and certain types of squamous cell carcinoma.

While chronic kidney disease, dehydration, and liver dysfunction can alter calcium levels, they are not the primary causes of hypercalcemia. In fact, chronic kidney disease often leads to hypocalcemia due to impaired renal function and altered vitamin D metabolism. This makes primary hyperparathyroidism or malignancy the most common direct causes of hypercalcemia in the veterinary setting.