Why does my dog have high blood calcium? 

Have you just been told that your dog’s blood calcium levels are too high? It can be hard to process and understand all the information your vet gives you, especially if you feel stressed about your pet’s health.  

While your vet should always be your first port of call for more information about your dog’s condition, we are also here to help! In this article, we’re going to explore blood calcium levels in more detail, including what the possible causes are and what your vet might need to do next.  

Why is there calcium in my dog’s blood? I thought it was for bones and teeth 

When most owners think of calcium, they think of bones and teeth. And rightly so! Calcium combined with phosphorus makes hydroxyapatite, a mineral complex that gives strength to bones and teeth. The right balance of calcium and phosphorus is therefore crucial in growing puppies to avoid limb deformities. Most of the body’s calcium is stored in the bones.  

However, calcium is also found in much lower amounts elsewhere in the body, in cells or flowing through the blood. Calcium is involved in many other processes in the body, too, including – 

Blood calcium can either be bound to proteins or unbound (ionised) and biologically active. Added together, these make the total calcium level found on many routine blood tests. 

Blood ionised calcium (iCa) levels are normally strictly regulated in an act known as calcium homeostasis. Parathyroid hormone, secreted by the parathyroid glands in the neck, helps to regulate calcium levels alongside two other hormones, calcitonin and 1,25-dihydroxyvitamin D3.  

Calcium-sensing receptors at various points around the body detect any changes in blood iCa levels. These act on different cells to cause either a reduction or an increased level of iCa as needed, keeping levels steady.  

But sometimes disruptions to this feedback loop occur, meaning that levels of blood calcium become too high (hypercalcaemia) or too low (hypocalcaemia). 

Causes of high blood calcium (hypercalcaemia) 

There are many reasons why a dog’s blood calcium could be too high.  

The following list is not complete but features some of the most commonly seen issues in dogs  – 

Inappropriate diet  

A diet that has been incorrectly formulated could be too high (or too low) in essential nutrients, leading to dietary imbalances 

Primary hyperparathyroidism  

Too much parathyroid hormone is excreted by the parathyroid glands in primary hyperparathyroidism, causing an elevation in blood calcium. This is often caused by a benign tumour or tissue overgrowth on the parathyroid gland, known as an adenoma. A very small percentage of cases can be caused by a more sinister malignant tumour known as a parathyroid carcinoma.   

Cancer  

Various malignant cancers can cause elevations in blood calcium levels. This is because certain tumours produce something called parathyroid hormone-related protein (PTHrP), which mimics the action of parathyroid hormone. The most common examples include lymphoma, anal sac adenocarcinoma, thymoma and bone tumours. Other cancers that may also raise blood calcium levels include mammary tumours and pancreatic cancer. Cancer is the most common cause of hypercalcaemia in dogs, accounting for nearly 50% of cases.  

Kidney disease  

Both acute (sudden onset) kidney disease from toxicity or obstruction, and chronic kidney disease can cause hypercalcaemia. This is because the kidneys are no longer able to do their job of getting rid of excess phosphorus effectively, causing blood phosphorus levels to rise. Calcium starts leaving the bones to try and balance phosphorus levels. This causes a rise in blood calcium, weakens the structure of the bones and causes deposits of inflammation, causing crystals around the body.  

Hypervitaminosis D  

Ingesting too much vitamin D can cause a rise in blood calcium levels. Examples of products that could cause this toxicity include anti-psoriasis cream, salmon oil, and some rat poisons.  

Granulomatous disease  

Certain infections can raise calcium levels in the blood. This can include fungal infection, parasitic infection and skin infections. 

Skeletal disease  

As well as bone tumours, other diseases in the bone can also raise blood calcium. Examples include osteomyelitis (bone infection) and hypertrophic osteodystrophy. 

Sometimes we can see high iCa in the blood due to issues with sampling or laboratory error. Plus, we can see elevations which are transient, meaning that high levels do not last long and are due to other underlying issues such as dehydration (haemoconcentration). 

What are the symptoms of high blood calcium? 

Hypercalcaemia can cause severe disturbances in normal body functions.  

The symptoms of hypercalcaemia may be related to high calcium levels directly or to the underlying disease process. The symptoms seen will also depend on how long the problem has been going on. In many cases, signs go unnoticed by owners altogether, with high calcium just turning up on a routine blood test. 

Possible symptoms of high blood calcium include – 

Investigation of high blood calcium 

If hypercalcaemia is found on a blood test, then your vet will need to try and work out what the underlying cause is. To do this, they may need to perform several tests – 

History and physical examination 

A thorough history will be taken from you, discussing possible symptoms like changes in thirst, your dog’s diet, travel history and any possible exposure to toxins. A physical examination will also be performed. The vet should carefully feel your dog’s lymph nodes to assess for any signs of enlargement, check their mammary glands and even perform a rectal exam to feel for any anal sac tumours. They may assess your dog for any lameness or bone pain, too. They will also check routine parameters like their heart rate and temperature, as well as record their body weight.  

Depending on your vet’s findings, the history and physical examination could dictate which tests are needed next.  

Blood tests 

Hypercalcaemia is often first noticed on a general blood test. Your pet may have had a blood test as a routine health screen or because they were showing vague symptoms of being unwell.  

As well as looking at your pet’s total calcium levels, general biochemistry, electrolytes and haematology panels are often run on an initial blood screen. Biochemistry helps to highlight any changes in liver and kidney values, blood sugar and protein levels. Haematology assesses red cell numbers for anaemia and white cells for signs of infection and inflammation. Electrolytes include calcium, phosphorus and potassium. If your vet is missing any of this information from the first blood sample, they may advise running these tests before moving on. 

They will also want to check whether the high calcium level is repeatable, and not just a passing (transient) issue. So, it is common to repeat the total calcium blood test to check this.  

If the total calcium is still high, then your vet may then suggest running a more specific ionised calcium blood test, as well as tests that measure the parathyroid hormone levels and parathyroid hormone-related protein (PTHrP). This will help to determine if the underlying disease is related to a problem with the parathyroid gland or something else.  

Diagnostic imaging  

If a problem with the parathyroid gland is suspected, then an ultrasound scan of the neck can be useful to look for a parathyroid tumour. 

However, sometimes your vet needs to go on a bit more of a search. X-rays of the chest may be advised, with 3 different views needed to fully assess the lungs for any changes. This can help to identify primary tumours but also metastasis (the spread from a tumour elsewhere in the body).  

Abdominal ultrasound is also recommended to perform a detailed assessment of any abnormal organs or lymph nodes. Computed tomography (CT scans) can also be helpful when trying to find an underlying cause for hypercalcaemia.    

If your dog has a limp or a suspected bone tumour, then X-rays of the affected area would be recommended too. 

Sampling 

If any suspicious changes are found in the lymph nodes, bones or organs on diagnostic imaging, then samples can be taken. Fine needle aspirates collect cells to send to the laboratory for analysis. This will give your vet more information about whether they have found a tumour, as well as how malignant it might be. Your vet may also need to take samples from organs that appear normal to check for the presence of any cancerous cells. 

Treatment of hypercalcaemia  

We can’t go into great detail about the treatment for hypercalcaemia, as this will depend on the underlying cause.  

If your dog has only mildly elevated calcium levels and they otherwise seem well, they may not require any immediate treatment while investigations are taking place. However, if they have very high levels or are very sick, then intervention could be needed. 

Your vet will take steps to immediately try and reduce your pet’s blood calcium levels to limit damage. This could include hospitalisation on a drip for fluid therapy, which will help calcium to be flushed out by the kidneys. Various medications can also be helpful to further encourage calcium loss in the urine, counteract the effects of vitamin D, reduce absorption of calcium from the gut and decrease calcium being mobilised from the bones.  

Long-term management of your dog’s issues will depend on their diagnosis, but could involve surgery, chemotherapy or dietary changes. 

Sadly, in the case of metastatic cancer or end-stage kidney failure, the long-term prognosis is poor. Euthanasia may be advised on welfare grounds if your dog’s quality of life is deteriorating.   

Summary  

Calcium balance is complicated, and our dogs usually do a good job of keeping their levels in check. If your dog has high blood calcium levels, then your vet will need to do some more tests to work out the underlying cause. Hypercalcaemia may be an indication of serious disease, and treatment will very much depend on your pet’s diagnosis.  

If you have any questions about your dog’s condition, then don’t hesitate to speak to your vet. They will be happy to answer your questions and explain their diagnostic and treatment plan to you in more detail.