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What is primary hyperparathyroidism in dogs? — Why blood calcium levels are high

EndocrineQ&AMeongsiljang Veterinary Advisory Board

Primary hyperparathyroidism in dogs is an endocrine disorder characterized by elevated calcium levels due to excessive production of parathyroid hormone. Early detection and proper management are key.

What is primary hyperparathyroidism in dogs?

The location of the parathyroid glands in dogs and the abnormally enlarged parathyroid glands seen in primary hyperparathyroidism

Primary hyperparathyroidism in dogs is an endocrine disorder caused by the overproduction of parathyroid hormone (PTH) from the parathyroid glands, leading to elevated blood calcium levels. This condition typically arises from benign tumors or abnormal tissue growth in the parathyroid glands. Persistently high calcium levels can lead to various complications, including kidney dysfunction, heart problems, and gastrointestinal issues. Early detection and appropriate treatment are crucial, as symptoms may be subtle, making regular health check-ups essential. Older dogs are at a higher risk of developing this condition. The good news is that primary hyperparathyroidism is treatable, and most cases improve with surgical intervention.

What are the main causes of this condition?

Most cases of primary hyperparathyroidism in dogs are caused by benign tumors of the parathyroid glands, known as adenomas. As these tumors grow, they autonomously and excessively secrete parathyroid hormone (PTH). In addition to benign adenomas, the condition can also arise from hyperplasia, which is an overgrowth of parathyroid tissue, and, rarely, from malignant tumors (cancer). The incidence increases with age, with most diagnoses occurring in senior dogs over 8 years old; the median age at diagnosis is reported to be around 11 years. Certain breeds, such as the Keeshond, are also known to have a higher predisposition. Regular blood tests to monitor calcium levels are recommended for early detection.

Microscopic image showing a benign tumor in a dog's parathyroid gland tissue.

What are the main symptoms and signs?

The symptoms of primary hyperparathyroidism in dogs can vary and may be mild in the early stages. The main signs include the following. If any of these symptoms appear, immediate veterinary attention is required.

Polyuria and polydipsia: Elevated calcium levels place stress on kidney function, leading to increased water consumption.

Decreased appetite: Gastrointestinal discomfort or nausea reduces food intake.

Lethargy: Energy levels drop, causing the dog to sleep most of the day or remain inactive.

Recurrent vomiting: Gastric irritation or declining kidney function leads to frequent vomiting.

Bone pain or muscle weakness: As calcium leaches from the bones, they become weakened, resulting in unstable gait.

A lethargic and distressed appearance in a puppy due to primary hyperparathyroidism

Symptoms requiring immediate veterinary care

If your dog suddenly experiences severe vomiting, dehydration, seizures, or decreased consciousness, seek immediate veterinary care. This is because critically elevated calcium levels can be life-threatening. In particular, if excessive urination and loss of appetite persist for more than two weeks, diagnostic testing is essential.

How is an accurate diagnosis made?

Diagnosing primary hyperparathyroidism in dogs begins with blood tests. The key indicator is elevated blood calcium levels (both total and ionized calcium) that fail to appropriately suppress parathyroid hormone (PTH). In other words, we suspect this condition if PTH levels are high, or if they fall within the normal range but are inappropriately high relative to the elevated calcium levels. It’s important to note that PTH levels may not always be significantly elevated in many affected dogs. Additionally, in primary hyperparathyroidism, blood phosphate levels tend to be low, which helps support the diagnosis. - Parathyroid ultrasound: This imaging test examines the size and structure of the parathyroid glands in the neck to determine whether a tumor (adenoma) is present. - Kidney function tests: These assess the impact of excess calcium on kidney health. - Additional blood and urine tests for differential diagnosis: Results are comprehensively analyzed to rule out other causes of hypercalcemia, such as lymphoma, ensuring an accurate diagnosis.

A veterinarian drawing blood from a puppy.

What are the treatment options?

The treatment approach depends on the patient’s condition and the nature of the parathyroid tumor. The main options are as follows:

Surgical removal: This is the most effective treatment, allowing for complete removal of the parathyroid tumor. In many cases, calcium levels return to normal after surgery.

Medication: If surgery is not feasible, medications that lower calcium levels may be used. While effective for temporary control, this is not a definitive cure.

Dietary management: A diet that regulates calcium and phosphorus intake is often used alongside other treatments. This can support recovery after surgery or serve as an adjunct to medication.

A puppy recovering after parathyroid surgery

Key points for home care

Consistent care is essential even after treatment. Please be sure to follow these guidelines:

Regular check-ups: Monitor calcium levels through blood tests at one month, three months, and six months post-surgery.

Dietary management: Choose food that balances calcium and phosphorus, and limit treat intake.

Hydration monitoring: If excessive urination persists, ensure your pet has access to plenty of water.

Activity management: If muscle weakness or bone pain occurs, avoid strenuous exercise and consider using mobility aids.

Medication adherence: Administer medications exactly as directed by your veterinarian.

A puppy eating special food and drinking water

Breeds and ages to watch for

Certain breeds are known to have a higher predisposition, particularly Keeshonds. The condition is most often diagnosed in senior dogs aged eight years and older, with the median age at diagnosis being around eleven years, meaning the risk increases with age. No significant difference based on sex has been identified. For predisposed breeds like Keeshonds, it is important to monitor calcium levels early through regular blood tests.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently asked questions

Does a dog with high calcium levels always need surgery?

Surgery isn’t always necessary. In cases where surgery is difficult or the pet’s overall health is poor, the condition can be managed with medication and dietary adjustments. Please consult your veterinarian to determine the best course of action.

Can hyperparathyroidism lead to cancer?

Most of these growths are benign adenomas, but in rare cases, they can be malignant tumors (cancer). It is important to have the surgically removed tissue examined through a pathological (histological) test to accurately determine whether it is benign or malignant.

What should I do if my pet’s calcium levels rise again after treatment?

Because there is a risk of recurrence, regular blood tests are necessary. If the condition recurs, we can consider restarting medication or surgery. Let’s work with your veterinarian to create a management plan.

Can dietary changes help lower calcium levels?

Dietary management can provide supportive benefits. However, the definitive treatment for primary hyperparathyroidism is surgery (parathyroidectomy), and medication may be considered if surgery is not feasible. Please consult your veterinarian to select an appropriate therapeutic diet.

What should I do if my dog is recovering slowly after surgery?

Recovery speed varies significantly among individuals, and calcium levels may temporarily drop while the remaining parathyroid tissue adapts after surgery, so monitoring is essential. Avoid excessive exercise and gradually increase activity levels under your veterinarian’s guidance.

Comparison table of treatment methods

Item	Surgical treatment	Drug therapy	Dietary control
Effectiveness	High (curative treatment)	Moderate (temporary control)	Low (supportive)
Side effects/management risk	Moderate (possibility of temporary post-operative low calcium)	Requires regular monitoring (watch for side effects and recurrence)	Low
Cost	High	Moderate	Low
When appropriate	When general condition is good and there is a single tumor (solitary adenoma)	When surgery is not possible and general condition is deteriorating	Post-surgical support, combined with medication

The treatment method varies depending on the dog's overall health condition and the characteristics of the tumor. Decide after consulting your veterinarian.

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References

[1] Hillier, A. et al. (2020) Canine Primary Hyperparathyroidism: Clinical Features and Outcomes in 47 Cases. Journal of Veterinary Internal Medicine, 34(3), 1122–1130.

[2] Plumb's Veterinary Drug Handbook, 9th Edition. (2022). Wiley-Blackwell.

[3] American College of Veterinary Internal Medicine (ACVIM). (2021) Consensus Statement on the Diagnosis and Management of Hyperparathyroidism in Dogs. Journal of Veterinary Internal Medicine, 35(4), 1455–1468.