Hyperparathyroidism in Dogs: Symptoms, High Calcium & Treatment (2026)

Q: What is hyperparathyroidism in dogs?

Hyperparathyroidism is a condition in which one or more parathyroid glands produce excessive parathyroid hormone (PTH). PTH normally raises blood calcium by pulling it from bones, increasing reabsorption in the kidneys, and stimulating vitamin D activation. When PTH is overproduced, blood calcium climbs too high. There are two main forms: primary (a benign parathyroid tumor secreting PTH autonomously) and secondary (the glands react appropriately to low calcium caused by kidney disease or a poor diet, but the end result is still excess PTH activity).

Q: What are the symptoms of hyperparathyroidism in dogs?

Primary hyperparathyroidism (high calcium): excessive thirst and urination (polyuria/polydipsia), lethargy, muscle weakness, decreased appetite, vomiting, and constipation. Dogs may also develop calcium-containing bladder or kidney stones, which cause straining, blood in the urine, or recurrent urinary tract infections. Because signs develop slowly, many owners notice only vague changes in energy or water intake. Renal secondary hyperparathyroidism (often normal calcium): signs are driven more by the underlying kidney disease — PU/PD, weight loss, nausea, and in severe cases, softening of the jaw bones ('rubber jaw') from calcium being pulled from bone.

Q: What does bloodwork show with hyperparathyroidism in dogs?

Primary hyperparathyroidism: total calcium above 12 mg/dL (often 12–16 mg/dL), ionized calcium consistently elevated, phosphorus low or low-normal, and PTH that is normal or elevated — crucially, even a 'normal' PTH is inappropriate when calcium is this high (PTH should be near zero). Secondary renal hyperparathyroidism: PTH is elevated but calcium is usually normal or low-normal, phosphorus is elevated (from reduced kidney excretion), and BUN/creatinine are elevated. Measuring both PTH and ionized calcium together is the key to distinguishing primary from secondary disease.

Q: Is high calcium always from hyperparathyroidism in dogs?

No — cancer is actually the most common cause of hypercalcemia in dogs. Lymphoma, apocrine gland anal sac adenocarcinoma, multiple myeloma, and some carcinomas secrete PTH-related protein (PTHrP), which mimics PTH and raises calcium. Other causes include Addison's disease, granulomatous disease (fungal infections, histiocytic diseases), vitamin D toxicity (certain plants, rodenticides, some supplements), and idiopathic causes. Because the workup differs significantly, vets always check PTH and PTHrP, and often pursue cancer screening, before concluding a dog has primary hyperparathyroidism.

Q: How is primary hyperparathyroidism treated in dogs?

Surgery to remove the abnormal parathyroid gland (parathyroidectomy) is the definitive treatment. Success rates are high — most dogs are cured with a single surgery. The main post-operative complication is hypocalcemia (low calcium): when the tumor is removed, the remaining parathyroid glands — which have been suppressed for months — take time to recover. Dogs need close monitoring and often short-term calcium and calcitriol supplementation after surgery until the other glands resume normal function. Ultrasound-guided ethanol ablation of the tumor is an alternative to surgery in some cases.

Q: How is secondary hyperparathyroidism treated in dogs?

Treatment targets the underlying cause. For renal secondary hyperparathyroidism: phosphorus-restricted diet, phosphate binders (to reduce phosphorus absorption from food), and sometimes calcitriol supplementation to directly suppress PTH secretion. Treating the kidney disease itself slows PTH elevation over time. For nutritional secondary hyperparathyroidism (rare in dogs on commercial diets): correcting the diet to restore calcium-phosphorus balance allows PTH levels to normalize. The parathyroid glands themselves do not need to be removed in secondary disease.

Quick Facts: Hyperparathyroidism in Dogs

What it is: Overproduction of parathyroid hormone (PTH), leading to elevated blood calcium (hypercalcemia).
Primary form: A benign parathyroid adenoma secretes PTH autonomously; typically affects older dogs (age 8–13). Keeshonds have a known genetic predisposition.
Secondary form: Kidneys fail to excrete phosphorus → phosphorus rises → calcium falls → PTH rises to compensate. Common in dogs with chronic kidney disease.
Key bloodwork: Primary: high ionized calcium + low phosphorus + inappropriately detectable PTH. Secondary: high PTH + high phosphorus + normal/low calcium + elevated BUN/creatinine.
Most common cause of hypercalcemia in dogs: Cancer (lymphoma, anal sac tumor) — not hyperparathyroidism. Always rule out malignancy first.
Treatment: Primary: surgery (parathyroidectomy) is curative. Secondary: phosphate binders, restricted diet, calcitriol.
Post-surgical watch: Hypocalcemia after parathyroidectomy is the main risk — requires monitoring and short-term supplementation.

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What Is Hyperparathyroidism in Dogs?

Dogs have four tiny parathyroid glands — two pairs embedded near or within the thyroid glands in the neck. Their job is to regulate blood calcium by secreting parathyroid hormone (PTH). When calcium falls, PTH rises; when calcium normalizes, PTH shuts off. Hyperparathyroidism disrupts this feedback loop: PTH is produced in excess, driving blood calcium persistently higher than it should be.

High calcium sounds like it could be harmless, but hypercalcemia is toxic at sustained levels. It causes smooth muscle dysfunction (vomiting, constipation, poor bladder emptying), impairs kidney tubule function (leading to excessive urination), and promotes mineralization of soft tissues — including the kidneys themselves. Over time, untreated hypercalcemia can cause irreversible kidney damage.

“Hyperparathyroidism” covers two biologically opposite situations. Primary: the gland is broken and fires when it shouldn't. Secondary: the gland fires correctly in response to genuinely low calcium (from kidney failure or poor diet), but the downstream consequences are still harmful. Treatment is completely different for each — so distinguishing them is the first step.

Types and Causes

Primary Hyperparathyroidism

A single parathyroid gland develops a benign tumor (adenoma) that secretes PTH regardless of how high calcium rises. The feedback loop is broken. Approximately 85–90% of primary cases are single adenomas; parathyroid carcinoma (malignant) is rare in dogs. Primary hyperparathyroidism is most common in older dogs (mean age 10–11 years) and has no strong sex predisposition.

Keeshond dogs have a well-documented hereditary form caused by a mutation that leads to parathyroid hyperplasia rather than a discrete adenoma — affected dogs may present younger (as early as 3–5 years) and often have multiple glands involved.

Secondary Hyperparathyroidism

The parathyroid glands are working correctly — they are responding to genuine signals. The problem is upstream:

Type	Mechanism	Calcium Level
Renal secondary	CKD reduces phosphorus excretion → hyperphosphatemia → reduced calcitriol production → relative hypocalcemia → PTH rises	Normal or low-normal
Nutritional secondary	Diet too low in calcium or too high in phosphorus (e.g., all-meat diets) → chronically low calcium → PTH rises → bone resorption	Low or low-normal

Warning

High calcium in dogs: cancer until proven otherwise

In dogs, the most common cause of hypercalcemia is malignancy — particularly lymphoma and apocrine gland anal sac adenocarcinoma. These tumors secrete PTH-related protein (PTHrP), which has the same calcium-raising effects as PTH but is a completely different molecule. PTHrP is not measured on a standard PTH test. A full workup — including cancer screening, PTHrP assay, lymph node evaluation, and abdominal imaging — is standard before primary hyperparathyroidism is diagnosed.

Symptoms

Primary Hyperparathyroidism (Hypercalcemia)

Symptoms develop slowly over months as calcium creeps higher. Many dogs are diagnosed incidentally when a wellness panel shows elevated calcium before obvious symptoms appear.

Excessive thirst & urination

High calcium interferes with ADH signaling in kidney tubules — water pours out

Lethargy & weakness

Elevated calcium impairs neuromuscular transmission and smooth muscle function

Decreased appetite / vomiting

Hypercalcemia slows GI motility and can directly irritate the stomach

Constipation

Reduced GI smooth muscle tone slows colonic transit

Muscle weakness or stiffness

Prolonged hypercalcemia alters skeletal muscle membrane potentials

Urinary stones (calcium oxalate)

Excess calcium spills into urine → crystals form → painful, recurrent UTIs or obstruction

Recurrent UTIs

Stones create niches for bacteria; impaired bladder emptying worsens infection risk

Depression / behavior change

Neurological effects of persistent hypercalcemia

Secondary Hyperparathyroidism (Renal)

Because calcium is usually normal in renal secondary HPT, the hypercalcemic symptoms above are typically absent. Instead, clinical signs are driven by the underlying kidney disease: weight loss, nausea, reduced appetite, and increased thirst and urination. In severe, longstanding cases, excess PTH pulls calcium from bone tissue, causing:

Renal osteodystrophy: Bone demineralization, most visible in the skull and jaw
“Rubber jaw” (fibrous osteodystrophy): Jaw bones become soft and pliable — a late sign of severe, prolonged renal secondary HPT
Pathological fractures: Rare, but possible in extreme cases

What Bloodwork Shows

The key to diagnosing hyperparathyroidism is measuring both PTH and ionized calcium together and interpreting them in context. Neither value alone tells the full story.

Test	Primary HPT	Renal Secondary HPT
Total calcium	HIGH (>12 mg/dL)	Normal or low-normal
Ionized calcium	HIGH — the definitive finding	Normal or low
Phosphorus	LOW or low-normal (PTH suppresses renal reabsorption)	HIGH (kidneys can't excrete it)
PTH	Normal or elevated — both are inappropriate with high calcium	HIGH (appropriate response, but harmful)
BUN / Creatinine	May rise if hypercalcemia has damaged kidneys	HIGH — reflects underlying CKD
PTHrP	Undetectable (not a tumor marker for parathyroid)	Undetectable

Pro Tip

The ionized calcium vs. total calcium distinction

Total calcium on a routine panel includes calcium bound to albumin — which is inactive. Ionized (free) calcium is what actually drives physiological effects and is the clinically meaningful number. Dogs with low albumin (from liver disease, malnutrition) can have a falsely low total calcium even if ionized calcium is fine — and vice versa. When a dog's total calcium is borderline or context is confusing, ionized calcium measurement is the most reliable test.

How Vets Diagnose It

Diagnosing primary hyperparathyroidism in dogs is a process of exclusion as much as confirmation, because many conditions raise calcium.

Confirm true hypercalcemia

Recheck total calcium and measure ionized calcium. Rule out lab error, lipemia, and low-albumin states (which falsely lower total calcium). If ionized calcium is consistently elevated on two separate samples, true hypercalcemia is confirmed.

Screen for cancer

Thorough lymph node palpation and aspiration, chest X-rays, abdominal ultrasound, and rectal exam (for anal sac masses). PTHrP measurement helps identify humoral hypercalcemia of malignancy. Complete blood count may show circulating abnormal lymphocytes in lymphoma.

Check for other causes

Addison's disease workup (ACTH stimulation test), urine culture for granulomatous disease, medication/supplement history (vitamin D toxicity), and review for other systemic illness.

Measure PTH and PTHrP together

An elevated or even normal PTH with high ionized calcium points strongly to primary hyperparathyroidism (cancer would produce PTHrP, not PTH; and a normal parathyroid would suppress PTH to near-zero with high calcium). Low PTH with high calcium points to non-PTH-mediated causes.

Cervical ultrasound to find the adenoma

A skilled ultrasonographer can often visualize a parathyroid adenoma as a small, hypoechoic nodule adjacent to or within the thyroid. This is used both to confirm the diagnosis and to plan surgery. Nuclear scintigraphy is used in some referral centers for difficult-to-locate tumors.

Treatment

Primary Hyperparathyroidism: Surgery

Parathyroidectomy — surgical removal of the abnormal gland — is the standard and curative treatment. The surgeon identifies and removes the adenoma (often only one gland is involved) while leaving the remaining three glands intact. Success rates are excellent in dogs.

Post-operative hypocalcemia is the most important complication. When the adenoma is removed, calcium drops — sometimes rapidly. The remaining parathyroid glands have been suppressed for so long that they cannot immediately ramp up PTH production. Dogs typically require:

Hospitalization for 24–72 hours post-surgery with frequent calcium checks
Oral calcium carbonate supplementation for days to weeks
Calcitriol (active vitamin D) to support calcium absorption until the remaining glands recover

Signs of post-op hypocalcemia to watch for at home: facial rubbing, muscle twitching or tetany, stiff gait, hypersensitivity to touch, or seizures. These are manageable if caught early.

Ultrasound-guided ethanol ablation — injecting alcohol directly into the adenoma under ultrasound guidance — destroys tumor tissue without surgery. It is used for dogs that are poor surgical candidates or when the tumor is clearly visible on ultrasound. Multiple treatments may be needed and it carries a small risk of damage to surrounding thyroid or parathyroid tissue.

Secondary Hyperparathyroidism: Medical Management

The parathyroid glands do not need to be treated — they are responding correctly. Treatment targets the cause:

Phosphate-restricted diet

Kidney-support diets (e.g., Hill's k/d, Royal Canin Renal) are formulated with reduced phosphorus. Less dietary phosphorus means less phosphorus for the kidneys to struggle with, which reduces the cascade that drives PTH secretion.

Phosphate binders

Given with meals to bind dietary phosphorus in the gut before it is absorbed. Options include aluminum hydroxide, calcium carbonate, lanthanum carbonate, and sevelamer. Binders are added when diet alone does not adequately control phosphorus levels.

Calcitriol supplementation

Failing kidneys produce less active vitamin D (calcitriol), which normally suppresses PTH secretion. Supplementing calcitriol directly reduces PTH levels. Must be used cautiously — excess calcitriol causes hypercalcemia. Requires careful monitoring.

Nutritional secondary hyperparathyroidism is uncommon in dogs eating commercial complete diets, but can occur with all-meat home-cooked diets (very high phosphorus, low calcium) or improperly formulated raw diets. It is more common in puppies, because their rapidly growing bones demand more calcium. Treatment is dietary correction — switching to a properly balanced diet. PTH normalizes once calcium-phosphorus balance is restored.

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Monitoring After Treatment

After Parathyroidectomy (Primary HPT)

Calcium checked every 12–24 hours in hospital post-surgery
Recheck ionized calcium and total calcium at 1–2 weeks post-discharge
Taper calcium and calcitriol supplementation as PTH from remaining glands recovers (typically over 2–8 weeks)
Long-term: annual calcium checks. Rare cases develop a second adenoma years later

Ongoing Monitoring for Renal Secondary HPT

Phosphorus levels every 3–6 months (target <4.5–5 mg/dL in CKD dogs depending on stage)
BUN, creatinine, and SDMA to track kidney function trajectory
Blood pressure monitoring — hypertension is common alongside CKD
Ionized calcium when using calcitriol — supplementation must not push calcium above normal

Diagnosing and treating hyperparathyroidism adds up — pet insurance can help

Between PTH and PTHrP testing, ionized calcium panels, cervical ultrasound, parathyroidectomy surgery, and post-operative calcium supplementation, primary hyperparathyroidism is a multi-visit, multi-test workup. Pet insurance can cover a significant portion of diagnostic and surgical costs.

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Frequently Asked Questions

What is hyperparathyroidism in dogs?

Hyperparathyroidism is overproduction of parathyroid hormone (PTH) by one or more parathyroid glands. PTH normally raises blood calcium — so excess PTH causes hypercalcemia. Primary hyperparathyroidism is caused by an autonomous tumor in the gland; secondary hyperparathyroidism is a compensatory response to low calcium from kidney disease or dietary imbalance.

What are the symptoms of hyperparathyroidism in dogs?

Primary hyperparathyroidism (high calcium): excessive thirst and urination, lethargy, muscle weakness, poor appetite, vomiting, and constipation. Calcium-containing urinary stones (calcium oxalate) are a common complication. Signs develop gradually and are often mistaken for normal aging. Renal secondary hyperparathyroidism: signs are driven by kidney disease — weight loss, nausea, PU/PD — and in severe cases, jaw bone softening ('rubber jaw') from calcium resorption.

What does bloodwork show with hyperparathyroidism in dogs?

Primary: high total calcium (often 12–16 mg/dL), high ionized calcium, low phosphorus, and an inappropriately normal or elevated PTH (any detectable PTH with high calcium is abnormal). Secondary renal: high PTH, elevated phosphorus, elevated BUN/creatinine, and usually normal or low-normal calcium. Measuring PTH alongside ionized calcium is the key to distinguishing primary from secondary disease.

Is high calcium always from hyperparathyroidism in dogs?

No — cancer (lymphoma, anal sac adenocarcinoma, myeloma) is the most common cause of hypercalcemia in dogs. These tumors secrete PTH-related protein (PTHrP), not PTH itself. Other causes include Addison's disease, granulomatous infections, and vitamin D toxicity. The full workup — including PTHrP, PTH, and cancer screening — is needed before concluding a dog has primary hyperparathyroidism.

How is primary hyperparathyroidism treated in dogs?

Surgery (parathyroidectomy) to remove the abnormal gland is curative in most cases. Post-operative hypocalcemia is the main risk — the remaining glands have been suppressed and need time to recover. Short-term calcium and calcitriol supplementation is usually required after surgery. Ultrasound-guided ethanol ablation of the tumor is an alternative for poor surgical candidates.

How is secondary hyperparathyroidism treated in dogs?

Treatment targets the underlying cause. For renal secondary HPT: phosphorus-restricted diet, phosphate binders, and sometimes calcitriol to directly suppress PTH. For nutritional secondary HPT: correcting the diet restores normal PTH. The parathyroid glands themselves are not removed in secondary disease — they are responding appropriately; the problem is upstream.

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