Feline idiopathic hypercalcaemia: first treatment step
8-year-old longhaired cat with moderately high ionised calcium on several measurements over months and a calcium oxalate bladder urolith. Neoplasia, kidney disease and vitamin D toxicity have been ruled out.
| Parameter | Result | Reference |
|---|---|---|
| Ionised calcium | 1.52 mmol/L | 1.10–1.40 |
| Phosphorus | 4.8 mg/dL | 3.0–6.5 |
| PTH | Undetectable | 0.4–2.5 pmol/L |
| PTHrP | Not detectable | < 1.0 pmol/L |
| Creatinine | 1.6 mg/dL | 0.8–2.0 |
What is the most reasonable first therapeutic step?
chevron_right Show answer and explanation
A. Switching to a high-fibre or renal diet, non-acidifying, and rechecking ionised calcium in a few weeks
Correct. Feline idiopathic hypercalcaemia is first treated with diet: fibre reduces intestinal calcium absorption, and renal diets provide less calcium and phosphorus. Some cats normalise with this change alone.
B. Exploratory parathyroidectomy
PTH is suppressed, which shows that the parathyroids are responding normally to the hypercalcaemia and are not its cause.
C. Oral alendronate from the outset
It is effective, but it is reserved for cats that do not respond to diet or prednisolone, because it is lifelong treatment with demanding administration and possible adverse effects.
D. Long-term oral furosemide
It increases urinary calcium excretion, favouring new calcium oxalate uroliths, and predisposes to dehydration. It only makes sense in acute management with fluids.
lightbulb Key takeaway
Idiopathic hypercalcaemia is the most common cause of ionised hypercalcaemia in cats and is a diagnosis of exclusion (rule out neoplasia, kidney disease, hyperparathyroidism and vitamin D). The usual sequence is diet, then prednisolone and, if that is not enough, alendronate. Avoid acidifying diets and watch for oxalate uroliths.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.