Cat & Dog - Calcium Blood Levels

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 situated just below the larynx (voice box), near the trachea (windpipe).  If circulating calcium levels 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 problems result if the circulating calcium is incorrect?

Due to its many functions in the body, incorrect calcium levels have profound effects:

• Hypocalcaemia: Low levels of circulating calcium can result in muscle twitching, loss of appetite, weakness and listlessness.  In severe cases, there may be convulsions (seizures).   Low blood calcium levels are most commonly found in nursing bitches feeding a large litter of puppies.  The puppies drain on 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.  Other causes of hypocalcaemia include antifreeze (ethylene glycol) poisoning, inflammation of the pancreas, kidney failure or failure of the parathyroid glands themselves.
• Hypercalcaemia: Hypercalcaemia (excess circulating blood calcium) can result in weakness, listlessness, increased drinking and urination together with loss of appetite.  With some animals, prolonged hypercalcaemia may be responsible for the formation of bladder or kidney stones.  Hypercalcaemia may signal the presence of serious underlying disease including failure of the kidneys, adrenals, Addison's disease, parathyroid gland tumour and/or other tumours.

What tests are required?

A single blood sample can be used to measure total circulating calcium.  Sometimes the level of ionised circulating calcium is also measured.

What further tests may be necessary?

If hypercalcaemia or hypocalcaemia is present, other tests may be necessary.  These can include tests to measure parathyroid hormone levels.