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Cat health

Hypercalcaemia in cats


Hypercalcaemia is defined as an abnormally high amount of calcium in the blood.

Calcium plays an essential role in numerous biochemical pathways, and adequate amounts are required for cell growth, muscle tone and contraction, blood coagulation, and cell membrane stability.  In healthy individuals, calcium absorption from the intestinal tract, calcium release from bone, and calcium conservation or excretion by the kidneys are all carefully regulated to optimise calcium concentrations.

Common causes of hypercalcaemia in cats include:

  • Chronic kidney disease
  • Certain cancers - such as lymphoma, thyroid carcinoma, anal sac carcinoma, mammary tumours
  • Hyperparathyroidism - increased production of a hormone produced by the parathyroid gland located in the neck
  • Rarely certain plants, rodenticides, and human psoriasis creams can cause hypercalcaemia in cats

In some cases, despite thorough testing an underlying cause is not found (Idiopathic)

Clinical signs

Clinical signs are often vague and non-specific, such as lethargy, depression, and poor appetite. Other changes include an increase in thirst and urination, difficulty urinating, blood in the urine, or abdominal pain secondary to calcium-containing kidney stones. Vomiting and constipation can occur. In severe cases, muscle weakness, twitching and seizures may be seen.


The first sign we will notice will be on a blood test. The calcium level we run on our routine tests may not show the true value as it shows the total calcium level, which can sometimes still be normal. We are mainly interested in the calcium available in the body, known as the ionised calcium (iCa). We are able to run a test for the iCa in the clinic on a different machine to check for true hypercalcaemia. From there, we need to try find the cause of the hypercalcaemia.

In most cases, a diagnosis will be based on a physical examination, blood and urine tests, x-rays of the chest and abdomen, and an ultrasound of the abdomen and neck. Specific tests to assess parathyroid hormone level may also be performed. If we do not find anything, we assume they have idiopathic hypercalcaemia


Appropriate treatment will depend on the cause of the hypercalcaemia. In cats with idiopathic hypercalcaemia (no identifiable cause), diet modifications and medication can be prescribed to reduce blood calcium levels.

One medication that may be used is Alendronate (a bisphosphonate). If your cat is taking this medication it is important to fast them for 8-12 hours prior to administering, and to always follow with a small volume of water to prevent irritation to the oesophagus. Food can then be provided 60 minutes after administration.

Cats receiving alendronate therapy should be monitored for vomiting or regurgitation, heart irregularities, and muscle spasms. Blood tests should be performed regularly to monitor their calcium levels. If you have any concerns, please contact the clinic immediately.

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