Calcium (Ca)
Electrolytes & minerals ·Also called: Ca, calcium, total calcium, ionised calcium, hypercalcaemia
What it is
Calcium circulates in two forms: bound to proteins, and free — the ionised fraction, which is the biologically active part. Standard panels measure both together as total calcium; a separate ionised calcium test measures only the active portion.
Why your vet measures it
A persistently high calcium in a dog or cat is one of the findings that most often leads to a cancer diagnosis, so it is rarely left uninvestigated. A low ionised calcium causes tremors and, in nursing mothers, full-blown seizures that need emergency treatment.
What a high result can mean
- Cancer — lymphoma and anal sac carcinoma in dogs are the classic causes
- Primary hyperparathyroidism, a benign parathyroid gland tumour
- Kidney disease
- Vitamin D toxicity from rodenticide, supplements, or human psoriasis creams licked off skin
- Hypoadrenocorticism (Addison's disease) in dogs
- Normal bone growth in puppies and kittens
What a low result can mean
- Low albumin, which lowers total calcium without affecting the active fraction
- Eclampsia in a nursing mother — an emergency causing tremors and seizures
- Antifreeze (ethylene glycol) poisoning
- Acute pancreatitis
- Accidental damage to the parathyroid glands during thyroid surgery in cats
Dogs and cats differ
In dogs, a persistently high calcium prompts a search for lymphoma and a rectal examination for an anal sac tumour. In cats, high calcium is more often idiopathic — genuinely unexplained after investigation — and is managed with diet and monitoring.
Questions worth asking your vet
- Should we measure ionised calcium to confirm this?
- Is the albumin low, and could that explain a low total calcium?
- If it is genuinely high, what are we looking for and how do we look?
Related terms
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