Calcium is widely found throughout the body and is required for many vital functions. It plays a role in many processes including cell growth, clotting of blood, nerve function, muscle contraction, hormone secretion, and bone formation to name a few.

The regulation of calcium concentration in the blood is complex and involves parathyroid hormone, vitamin D metabolites, and calcitonin (a hormone produced by the thyroid). These three "regulators" act together to maintain normal calcium levels in the blood and tissues of the body. Imbalances in the regulation of calcium can lead to a deficiency or an excess of calcium.

Hypercalcemia is a disorder in which there is excessive calcium in the bloodstream. Hypercalcemia can be a marker of an underlying disease and it can also lead to or create disease due to its toxicity to cells. 

Causes of Hypercalcemia

Hypercalcemia can be benign (e.g. it can be noted in young, growing animals, after a meal), however there are many diseases and conditions that can be associated with / cause hypercalcemia including:

  • Parathyroid disease
  • Cancer / malignancies
  • Kidney failure
  • Vitamin A or D toxicity
  • Skeletal diseases
  • Excessive consumption (calcium-containing supplements or medications)
  • Raisin or grape toxicity
  • Granulomatous disease (e.g. Blastomycosis, severe dermatologic disease)
  • Idiopathic (i.e. an underlying problem cannot be identified; more commonly identified in cats)  Learn more about Feline Idiopathic Hypercalcemia

Therefore, when hypercalcemia is identified in the course of performing blood tests, it often serves to cue the veterinarian that there could be a problem looming somewhere in the body.

Testing should be repeated (ensuring that the animal has been fasted) to prove it is a persistent problem on serial blood tests. If hypercalcemia is reproducible on subsequent blood tests, it's not uncommon for a veterinarian to then recommend a litany of tests to then try and identify the cause for hypercalcemia.

Signs of Hypercalcemia

Not all animals will demonstrate outward signs of this abnormality. However, some of the clinical signs include:

  • Polyuria / polydipsia (Increased urination and thrist)
  • Loss of appetite
  • Lethargy
  • Weakness
  • Vomiting
  • Constipation
  • Seizures or twitching
  • Bladder stones

Treatment of Hypercalcemia

The most important aspect is to identify and remove the underlying cause. In addition to managing the underlying issue, treatment of affected patients is largely supportive. Efforts are made to correct any concurrent dehydration and to reduce the levels of calcium in the blood. 

A variety of drugs may be considered depending on the overall condition of the pet. Treatment may include the use of diuretics, sodium bicarbonate, corticosteroids, drugs that prevent bone resorption, and others.

Complications / Effects of Hypercalcemia

In addition to the effects on the gastrointestinal tract, skeletal muscles, and central nervous system, there are can be effects on the heart. Arrhythmias (changes in the ECG) and possibly changes in blood pressure can be noted.