Hypercalcemia in Dogs

As little children our parents implore us to drink our milk so we will grow big and strong with healthy bones and pearly, white teeth. Later we are admonished to eat plenty of leafy greens and to consider taking calcium supplements as we start worrying about our aging, brittle bones. Manufacturers even fortify other food staples like orange juice, bread and cereal to get more calcium in our diets. That must mean that you or your dogs simply can’t get too much of this good thing, right?

Can a dog have too much calcium?
Unless you or your dog is taking supplements containing high doses of calcium, it is unusual to develop abnormally elevated calcium levels or hypercalcemia due to dietary intake. There are, however, many other medical situations/conditions where calcium levels can increase enough to result in serious and possibly life-threatening consequences — involving the other complex, physiological functions: blood clotting, nerve impulse conduction, and heart muscle contractions.

What causes elevated calcium levels in dogs?
The following is Dr. Mark E. Peterson’s top-10 list:

  • Spurious (fat in the serum causing false elevation of calcium)
  • Lymphosarcoma  
  • Hypoadrenocorticism (Addison's disease)
  • Primary hyperparathyroidism (parathyroid tumor)
  • Renal failure
  • Vitamin D toxicosis
  • Apocrine gland carcinoma (tumor) of the anal sac  
  • Multiple myeloma of bone (10-15% of cases have high calcium)
  • Other carcinomas (e.g., lung, mammary, nasal, pancreatic, thymic, thyroid, testicular)
  • Granulomatous diseases (caused by different infectious agents)

In addition, you should be aware that some drugs including certain diuretics and antacids and some rodenticides (rat poisons) can cause hypercalcemia so be sure your veterinarian is aware of any medications your dog is taking or might have had access to.

What are the signs of hypercalcemia in dogs?
Hypercalcemia is not common in any species but is encountered more often in dogs than in cats. As is so often the case in veterinary medicine, clinical signs of hypercalcemia can be very vague and nonspecific:

  • Increased thirst and urination
  • Decreased appetite
  • Lethargy and depression
  • Gastrointestinal upset causing vomiting
  • Abdominal pain and/or constipation

Kidney failure can occur as a result of hypercalcemia and then compound the problem as a further cause of imbalance. Disturbances in nerve conductivity and cardiac muscle contractions can ultimately cause neurologic tremors or seizures, weakness, and cardiac arrhythmias. If the levels remain significantly elevated, calcium can be deposited in any soft tissue or organ system in the body. Left untreated, hypercalcemia can be fatal.

Diagnosis and treatment of hypercalcemia
The first thing that should be done is a recheck blood test for calcium to verify that the level is, indeed, elevated and that the diagnosis of hypercalcemia is correct. Note that number one on Dr. Peterson’s list of likely causes was lab error. Furthermore, some calcium is bound to protein in the blood, some is complexed or connected to other compounds like bicarbonate while only about one-half of it is free, ionized calcium available for use. That means that the measured level also needs to be considered in light of your pet’s protein levels and acid-base status.

In the meantime, your veterinarian will want to decrease your pet’s blood calcium down to a safer (if not completely normal) level to avoid more serious consequences. This may be accomplished by the administration of high rates of intravenous fluids administration, diuretics, steroids or more specific calcium-regulating medications.  

Then, since hypercalcemia is a symptom of an underlying disorder, identifying the primary problem is of paramount importance for long term management and control. Sometimes a thorough history and a complete physical examination will narrow the list of possibilities and thus dictate the next diagnostic steps (blood work, XRays, aspirates, or biopsies of enlarged lymph nodes or palpable masses). Other times those tests will only serve to rule out the most common causes. In those cases more advanced tests (parathyroid hormone levels and ultrasound imaging) may be necessary to uncover the cause.

Once the final diagnosis is made, then, an appropriate and specific on-going treatment plan can be formulated.

If you have any questions or concerns, you should always visit or call your veterinarian -- they are your best resource to ensure the health and well-being of your pets.