Hypercalcaemia In Pets
Hypercalcaemia is the name for an elevated level of calcium in the blood. There are many possible causes of high calcium levels, and often, many tests are required to find the cause.
Although not an exhaustive list, causes of hypercalcaemia include:
- Hyperparathyroidism (overactive parathyroid gland)
- Cancers (including lymphoma or tumours of the anal sacs)
- Kidney disease
- Addison’s disease (hypoadrenocorticism; under-active adrenal glands)
- Vitamin D toxicity (caused by rodenticides, psoriasis cream, some plants)
- Other toxin ingestion (grapes/raisins, overdose of calcium supplements)
- Granulomatous disease
Clinical signs of hypercalcaemia include increased thirst and urination, lethargy and weakness. The severity of symptoms is often directly related to the degree of calcium elevation, with sudden rises (such as with toxin ingestion) causing more severe symptoms. If calcium levels get high enough, they can cause severe symptoms, or even prove fatal.
Many animals, however, show few symptoms at the point that the hypercalcaemia is diagnosed. More often, they are experiencing symptoms relating to the underlying cause of the hypercalcaemia, which prompts us to do blood tests and find the abnormal calcium level.
Calcium is found in three different forms in the body, the most relevant of which is called ionised calcium. Total calcium is most commonly measured on a routine blood test, however, this does not always correlate directly with ionised calcium levels. Total calcium can be a useful screening tool, but is not enough to make a diagnosis of hypercalcaemia. A high total calcium reading should be followed by measurement of ionised calcium. However, this requires a special machine, or to send a sample to an external laboratory using specific storage conditions, which is why it is not performed as a first-line test.
Due to the many causes of hypercalcaemia, a logical approach to diagnosis is required. Often, after confirming elevation of ionised calcium levels, a repeat clinical examination and history taking are performed. This will include questions about diet, medication, travel history, and any possible exposure to calcium-containing toxins. Physical examination will include careful palpation of the skin, mammary tissue and anal sacs for any growths.
It is likely that a full blood panel has already been carried out, but if not, this will be recommended to examine kidney function in particular. The hormone cortisol may be measured to check for Addison’s disease, if the dog has compatible symptoms. If there is no kidney disease present, further tests will be required:
Specific blood tests
Two specific blood tests are recommended, called parathyroid hormone (PTH) and parathyroid hormone related peptide (PRH-rP). Hyperparathyroidism is an uncommon condition, but causes increased secretion of PTH, which controls calcium levels in the body. PRH-rP is a protein which has the same effect as increased PTH, but is released by certain types of tumour. PTH and PTH-rp have to be measured at an external laboratory, and require samples to be rapidly frozen after collection before being precisely stored and transported.
Imaging
If PTH-rP levels are elevated, or this test is not performed, imaging is often recommended to look for cancers. This may include x-rays, ultrasound or CT, depending on the individual case. Most commonly, both the chest and abdomen are imaged.
Depending on the results of the above tests, additional diagnostics may be suggested. These could include urine analysis, further blood tests or biopsies. Your vet will explain the reasoning behind their advice. It is important to stress that finding a cause for hypercalcaemia can be complex, and often slow. Sometimes, referral to an internal medicine specialist or a centre with advanced imaging capabilities may be recommended.
The prognosis for cases of hypercalcaemia is variable, depending on the underlying cause. Hypercalcaemia due to toxicity generally has a good prognosis, though some pets will have long-term organ damage. For cases of primary hyperparathyroidism, surgery may be possible to remove the affected gland and offer a cure. Unfortunately, some cancers causing hypercalcaemia are not curable. However, chemotherapy or surgery may induce remission for some time. For pets with kidney disease, the prognosis is sadly more guarded, however, supportive care and home management strategies can extend life and keep pets comfortable.
The most important factor in prognosis is an accurate diagnosis. This will enable your vet to understand all possible treatment options, and help you decide what is most appropriate for you and your pet.
