Parathyroid & Calcium Problems in Dogs: Hypercalcemia & Hypocalcemia

Sep 29 • 10 min read

Your dog has started drinking water non-stop and asking to go out every hour. Or maybe it's the opposite picture: sudden muscle twitching, restlessness, and a worrying tremor that seems to come out of nowhere. Both pictures can trace back to the same tiny pair of glands in your dog's neck, and to one mineral doing too much or too little of its job: calcium.

Parathyroid and calcium problems in dogs happen when the body's calcium levels swing too high (hypercalcemia) or too low (hypocalcemia), usually because of a problem with the parathyroid glands or an underlying disease elsewhere in the body. High calcium causes increased thirst, urination, and weakness. Low calcium causes muscle twitching, tremors, and in severe cases, seizures. Both are diagnosed through blood tests and treated by addressing the underlying cause.

Key Takeaways

Calcium is essential for bones, muscle contraction, blood clotting, and nerve function, and the body works hard to keep its levels steady.
Parathyroid hormone, vitamin D, and calcitonin all work together to regulate blood calcium in your dog.
Hypercalcemia (high calcium) is most often linked to cancer, Addison's disease, or kidney disease in dogs, not to the parathyroid glands themselves.
Hypocalcemia (low calcium) is most often caused by chronic kidney disease, or by loss of parathyroid function, often after gland removal during other neck surgery.
Signs of high calcium include increased thirst and urination, poor appetite, and weakness. Signs of low calcium include muscle twitching, tremors, and seizures.
A dog with sudden muscle tremors or seizures related to low calcium needs emergency veterinary treatment with intravenous calcium.

What Do the Parathyroid Glands Actually Do?

Diagram showing how parathyroid hormone, vitamin D, and calcitonin regulate calcium in dogs

Your dog has small parathyroid glands sitting on either side of the thyroid gland in the neck. Despite their tiny size, they play an outsized role in keeping calcium levels steady throughout the body. Calcium isn't just about strong bones; it is also essential for muscle contraction, blood clotting, enzyme activity, the nervous system, and hormone release.

Three hormones work together as a team to keep blood calcium within a narrow, healthy range: parathyroid hormone, vitamin D, and calcitonin. Parathyroid hormone raises blood calcium by pulling it from bone, helping the kidneys hold onto more of it, and boosting calcium absorption from the gut. Vitamin D, which dogs must get from their diet rather than sunlight, works alongside parathyroid hormone to support calcium absorption. Calcitonin does the opposite job, stepping in to lower blood calcium when levels climb too high.

Think of this trio as a thermostat system for calcium. When something disrupts the balance, whether it's the parathyroid glands themselves or an unrelated disease elsewhere, calcium can swing too high or too low, and the effects ripple out to nearly every system in the body.

What Is Hypercalcemia (High Blood Calcium)?

Hypercalcemia means the level of calcium in the blood has risen too high. This excess calcium is harmful to tissues throughout the body, but it is especially damaging to the kidneys, nervous system, heart, and blood vessels. In severe cases, very high calcium levels can become life-threatening.

The signs your dog shows depend on how high the calcium level is, how quickly it rose, and how long it has been elevated. The most common signs are increased thirst and urination, followed by reduced appetite, vomiting, constipation, weakness, depression, muscle twitching, and seizures.

Importantly, in dogs, hypercalcemia is usually not caused by a problem with the parathyroid glands themselves. The parathyroid-driven form, called primary hyperparathyroidism, is relatively rare in dogs. Far more often, high calcium is linked to:

Cancer, especially lymphoma, anal sac tumors, and multiple myeloma
Addison's disease (hypoadrenocorticism), where up to 30% of affected dogs develop elevated calcium as part of the disease
Chronic kidney disease, through a mechanism that isn't fully understood
Vitamin D toxicity, from excess supplementation or accidental ingestion of certain rodent poisons or human psoriasis medications
Granulomatous disease, where certain infections trigger white blood cells to raise active vitamin D levels
Rarely, certain houseplants and bone tumors

Because so many different conditions can cause hypercalcemia, treatment starts with identifying and treating the underlying cause. Supportive treatment, such as intravenous fluids, diuretics, and glucocorticoids, is often used alongside this to bring calcium levels down more quickly while the root cause is addressed.

What Is Hypocalcemia (Low Blood Calcium)?

Hypocalcemia means blood calcium has dropped too low, and it primarily affects the nervous system and muscles. The hallmark signs are muscle twitching, tremors, and, in more severe cases, generalized seizures.

The most common causes of hypocalcemia in dogs include:

Hypoparathyroidism, where the parathyroid glands no longer produce enough parathyroid hormone, often following surgical removal of the glands during treatment for hyperthyroidism or a parathyroid tumor
Chronic kidney failure, probably the single most common cause of low calcium overall, though it doesn't usually cause the dramatic nervous system signs seen with hypoparathyroidism
Eclampsia, also called puerperal tetany, which affects nursing female dogs due to an imbalance between calcium intake and the calcium demands of milk production
Chelating agents, such as ethylene glycol found in antifreeze, which bind up calcium in the blood

Hypoparathyroidism specifically is uncommon in dogs, but it is important to recognize because it typically causes low calcium alongside high phosphate levels. Diagnosis relies on your dog's history and signs, blood tests showing this calcium and phosphorus pattern, and measurement of parathyroid hormone levels.

Signs to Watch For

Illustrated comparison of high calcium and low calcium signs in dogs

Because high and low calcium cause very different problems, it helps to know the signs of each:

Signs of high calcium (hypercalcemia):

Increased thirst and urination
Reduced appetite
Vomiting
Constipation
Weakness and depression
Muscle twitching in more advanced cases
Seizures in severe or prolonged cases

Signs of low calcium (hypocalcemia):

Muscle twitching and tremors
Muscle contractions or stiffness
Restlessness, nervousness, or agitation
Generalized convulsions or seizures
In nursing dogs specifically: trembling, heavy panting, stiff-legged movement, or disorientation, which points to a medical emergency called eclampsia

If your dog is nursing puppies and suddenly becomes stiff-legged, disoriented, or starts having tremors or seizures, this is an emergency. Eclampsia can progress quickly and needs immediate veterinary treatment.

How Are Calcium Disorders Diagnosed?

Diagnosis for both hypercalcemia and hypocalcemia starts with routine bloodwork to measure calcium levels, along with related values like phosphorus. Because so many different underlying conditions can cause abnormal calcium, your vet will often need additional tests to pin down the specific cause, which might include:

Blood tests for parathyroid hormone levels
Screening for cancer, including checking lymph nodes and the anal sac area
Kidney function tests
Testing related to Addison's disease if hypercalcemia is present
Vitamin D level testing if toxicity is suspected

Because the underlying cause of a calcium imbalance directly determines the treatment plan, your vet's goal is not just to confirm that calcium is abnormal, but to understand exactly why.

How Are Calcium Disorders Treated?

For hypercalcemia, treatment focuses on identifying and addressing the underlying condition. If a tumor is the cause, this may mean surgical removal or other cancer-specific treatment. If Addison's disease is the cause, treating the adrenal insufficiency itself typically normalizes calcium levels. If chronic kidney disease is involved, supportive care is the mainstay. Alongside treating the root cause, your vet may use intravenous fluids, diuretics, and glucocorticoids to help bring dangerously high calcium levels down more quickly.

For hypocalcemia, the immediate priority in a dog having muscle spasms or seizures is intravenous calcium to stop the crisis. Once stabilized, longer-term treatment usually involves dietary calcium supplements, often combined with vitamin D, to keep levels steady going forward. For hypocalcemia caused by chronic kidney failure specifically, treatment usually centers on dietary changes and medication to lower blood phosphate rather than aggressive calcium supplementation.

"Dietary supplements of calcium, often along with vitamin D, are prescribed for longterm treatment" of hypoparathyroidism in dogs. Merck Veterinary Manual, Disorders of the Parathyroid Glands and of Calcium Metabolism in Dogs

Why You Should Never Self-Treat a Calcium Problem

It might seem logical to reach for a calcium supplement the moment you hear the word "calcium problem," but this can do real harm. Giving calcium to a dog with hypercalcemia would make a dangerous situation worse. Even for dogs with confirmed low calcium, supplementation needs to be dosed precisely and paired with the right form of vitamin D, under a vet's guidance, since too much calcium given the wrong way carries its own risks, including for growing puppies.

This is exactly why routine bloodwork matters before starting any calcium supplement, and why an existing tremor, seizure, or excessive thirst and urination should always be diagnosed by a vet rather than treated with a guess at home.

Living With a Dog Managing a Calcium Disorder

Once the underlying cause of a calcium imbalance is identified and treatment begins, most dogs do well with consistent follow-up care. A few things help:

Keep all recommended follow-up bloodwork appointments, since calcium levels need to be rechecked to confirm treatment is working
Never start or stop a calcium or vitamin D supplement without your vet's direction, even if your dog seems better
Watch for a return of the original signs, whether that's increased thirst and urination or muscle twitching, and report any changes promptly
If your dog is a nursing mother, monitor closely in the weeks after whelping for any signs of eclampsia, since this can develop quickly

FAQ Section

Is high calcium in dogs always caused by the parathyroid glands?
No. Primary hyperparathyroidism is actually a relatively rare cause of high calcium in dogs. Far more often, high calcium is linked to cancer, Addison's disease, or chronic kidney disease. Your vet will need to look beyond the parathyroid glands to find the real cause in most cases.

What does low calcium look like in a dog?
The classic signs are muscle twitching, tremors, and, in severe cases, seizures. Some dogs also seem restless, nervous, or unusually agitated before these signs become obvious. If you notice sudden muscle twitching or a seizure, this needs immediate veterinary attention.

Can a calcium imbalance be an emergency?
Yes. Severely low calcium causing muscle spasms or seizures needs immediate treatment with intravenous calcium. Very high calcium can also become life-threatening if it isn't addressed. Both situations call for prompt veterinary care rather than a wait-and-see approach.

What is eclampsia in dogs?
Eclampsia, also called puerperal tetany, is a form of low calcium seen in nursing female dogs, caused by an imbalance between how much calcium is being used for milk production and how much is being taken in. Signs include trembling, heavy panting, stiffness, and disorientation, and it is treated as a medical emergency with intravenous calcium.

Should I give my dog a calcium supplement if I'm worried about their bones?
Not without veterinary guidance. Giving calcium supplements without a confirmed need can actually cause problems, particularly in growing puppies, where excess calcium can disrupt normal bone development. Always have your vet assess whether a supplement is appropriate before starting one.