Calcium Blood Levels - Why Is Testing Important?

Calcium is a mineral that is found in small quantities throughout the body. It plays an important role in many physical functions such as muscle contraction, transmission of nerve impulses, blood clotting and bone growth.

How are levels of calcium controlled in the healthy animal?

Calcium levels are controlled by the parathyroid glands. These small glands are associated with the thyroid gland which is situated just below the larynx, lying against the trachea (windpipe). If calcium levels in the blood are too low the parathyroids release parathyroid hormone which helps to restore calcium levels to normal. The mechanism involves Vitamin D and increased calcium absorption from the intestine. Once the calcium levels have returned to normal the amount of circulating parathyroid hormone is then reduced. 

What are the problems if the circulating level of calcium is too low or too high?

Due to its many functions in the body, incorrect calcium levels have many profound effects. Low levels of calcium (hypocalcaemia) can result in signs which include muscle twitching, loss of appetite, weakness and listlessness. In severe cases, there may be convulsions (seizures).  

Hypocalcaemia is most commonly found in nursing mothers feeding a large litter of puppies. The puppies drain the bitch's calcium supply, via the milk, causing a drop in her blood calcium. This is diagnosed by estimation of calcium blood levels and is easily corrected by injections of suitable calcium products. There are many other causes of hypocalcaemia including antifreeze (ethylene glycol) poisoning, inflammation of the pancreas, kidney failure or failure of the parathyroid glands themselves.

What happens when the blood calcium level is too high?

There may be subtle signs of illness as a result of hypercalcaemia (high calcium levels). These include weakness, listlessness, increased drinking and urination together with loss of appetite. In some pets prolonged hypercalcaemia may be responsible for the formation of bladder or kidney stones. 

High blood calcium levels may signal the presence of serious underlying disease including kidney failure, adrenal gland failure (Addison's disease), parathyroid gland tumours and some types of cancer.

How are blood calcium levels measured?

All that is needed is a single blood sample which can be measured to give an indication of the blood calcium level. This is called the total calcium. In some cases further tests may measure a more specific form of calcium called the ionised calcium. 

What further tests are then required?

Depending on whether the results show hypercalcaemia or hypocalcaemia sometimes other tests may have to be carried out. These may involve testing the levels of circulating parathyroid hormone since it is this hormone that directly controls circulating calcium levels.