Primary hyperparathyroidism (relatively rare in dogs)

Parathyroid glands are overactive (often due to a tumor) and secrete excessive parathyroid hormone

Removal or destruction of tumor

Hypercalcemia caused by cancer (malignant hypercalcemia)

Increased bone breakdown and resorption triggered by cancer cells causes higher levels of calcium in blood

Depends on specific type of cancer

Hypoadrenocorticism (Addison’s disease)

Multiple factors involved; up to 30% of dogs with Addison’s disease have increased calcium levels

Treatment of underlying disease normalizes calcium levels

Chronic kidney failure

Exact mechanism unknown

Supportive care

Vitamin toxicity

Vitamin D supplements taken in excess (for example, to treat hypoparathyroidism); accidental ingestion of calcipotriene (a human psoriasis medicine) or of rodent poisons containing calcitriol (no longer widely available in the US)

Adjustment of vitamin D dosage (if from medication); calcipotriene poisonings are often fatal

Granulomatous disease (masses of white blood cells that can form because of certain fungal and parasitic infections)

Inflammation activates the type of white blood cells that can increase levels of vitamin D

Treatment of underlying disease, for example, antifungal drugs or surgery

Houseplants (Cestrum diurnum [the day-blooming jessa-mine], Solanum malacoxylon, Triestum flavescens)

Contain substance similar to vitamin D that may cause hypercalcemia when accidentally eaten

Supportive care; corticosteroids

Bone tumors (rare)

Breakdown of bone increases blood calcium levels

Depends on specific type of cancer