CONDITION
Hyperparathyroidism in Dogs
Hyperparathyroidism describes a pattern in which the parathyroid glands—small structures near the thyroid in the neck—produce too much parathyroid hormone. This hormone normally regulates calcium levels in the blood, and when present in excess, it can pull calcium from bone and raise the amount circulating in the bloodstream. The condition can develop on its own (primary hyperparathyroidism, often linked to a small benign growth on one of the glands) or as a response to another process, such as kidney disease or dietary imbalance (secondary hyperparathyroidism). Owners may notice increased thirst and urination, reduced appetite, occasional vomiting, or a general loss of energy. Some dogs show no outward signs at all, and the pattern is identified only when blood tests reveal elevated calcium during routine screening or investigation of another concern. The signs, when present, tend to develop gradually and can be subtle in the early stages. This page explores what hyperparathyroidism may look like in a living dog, the mechanisms that drive changes in calcium and bone, how the condition is investigated through blood tests and imaging, and the range of approaches used depending on the underlying cause and the degree of disturbance.
Why this matters now
Primary hyperparathyroidism tends to appear in middle-aged to older dogs, often between eight and thirteen years, though younger animals can occasionally be affected. Certain breeds, including Keeshonds and other northern breeds, appear in clinical reports more frequently, though the condition can develop in any dog. Secondary hyperparathyroidism linked to kidney disease typically emerges alongside the progression of chronic kidney dysfunction, whilst nutritional secondary forms are more often seen in younger dogs fed unbalanced homemade diets low in calcium or high in phosphorus.
The disturbance in calcium regulation can develop slowly over months or even years, particularly in primary cases where a small parathyroid growth produces hormone at a steady but excessive rate. Some dogs show gradual worsening of signs such as increased thirst or reduced appetite, whilst others remain outwardly well for long periods and the pattern is revealed only through routine blood work. In secondary forms linked to kidney disease, the parathyroid response evolves in parallel with declining kidney function, and signs may reflect both the calcium disturbance and the underlying kidney disorder.
Signals & patterns
Early signals
Increased thirst and urination
Dogs may drink noticeably more water and need to urinate more frequently, sometimes overnight or in unusual places. This reflects the kidneys' response to elevated calcium, which interferes with their ability to concentrate urine.
Reduced interest in food
Appetite may decline gradually, with dogs eating smaller portions or skipping meals they would normally finish. High calcium can affect the stomach and intestines, contributing to a vague sense of nausea.
Quieter demeanour or lethargy
Energy levels may drop, with dogs spending more time resting or showing less enthusiasm for walks or play. This can be subtle and is easily attributed to other causes such as age or weather.
Occasional vomiting
Episodes of vomiting may occur sporadically, sometimes with no clear trigger. Elevated calcium can irritate the stomach lining and alter digestive function.
Later signals
Muscle weakness or stiffness
Some dogs develop a reluctance to jump, climb stairs, or move freely, reflecting progressive loss of calcium from bone or effects on muscle and nerve function. Movement may appear slower or more careful.
Weight loss
Gradual loss of body condition can occur as appetite remains poor and the metabolic disturbance continues. Muscle mass may decline alongside overall weight.
Excessive drinking despite intervention
Thirst may become pronounced and persistent, with dogs seeking water frequently throughout the day and night. This pattern can dominate daily routines and be difficult to ignore.
Click to read about the biological mechanisms
How this is usually investigated
Options & trade-offs
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