What is calcium and why is it important?
Calcium is a mineral that is found in small quantities throughout the body. It plays an important role in diverse and vital functions including muscle contraction, transmission of nerve impulses, blood clotting, and bone growth.
What is hypocalcemia?
The term hypocalcemia is used when the level of calcium in the blood is lower than normal (hypo = “below”, -emia = “blood”).
How are levels of calcium controlled in a healthy animal?
Calcium levels are controlled by a pair of parathyroid glands. These two tiny glands are embedded in the thyroid gland, which sits just below the larynx, or "voice box," overlying the windpipe.
The parathyroid glands are responsible for monitoring the level of calcium in the blood. When calcium levels are too low, the glands release a hormone called parathyroid hormone (PTH), which acts to return calcium levels to normal.
Why is having low calcium bad for my pet?
Low calcium levels are associated with a number of serious disorders including antifreeze poisoning, inflammation of the pancreas, kidney failure, and parathyroid gland failure. In nursing female dogs, heavy milk production can lead to hypocalcemia (milk fever) and may result in seizures.
Pets with abnormally low calcium levels often show signs of muscle twitching, loss of appetite, weakness, and listlessness. In severe cases, pets may have convulsions or seizures.
How is calcium measured?
Two forms of calcium are found the blood, called total calcium and ionized calcium (also called free calcium).
Total calcium. The test for total calcium is simple, rapid, and relatively inexpensive, and it is typically used as a preliminary test to measure calcium levels. However, total calcium can appear falsely decreased due to low levels of albumin (a blood protein that carries calcium around in the blood stream), as well as delayed testing (i.e., sample left standing on the counter for too long before testing). If preliminary testing reveals hypocalcemia, then measuring ionized calcium is often recommended to confirm the finding.
Ionized calcium. This is the definitive test for measuring blood calcium levels. It is an excellent test, but is more difficult to perform than total calcium, and requires patient preparation and special sample handling of the sample. It also tends to be more expensive and often takes longer to get results back from the laboratory.
What further testing is required if my pet has low total calcium on a routine blood test?
If a routine blood test reveals low total calcium, the test should be repeated to confirm the result, especially if albumin levels are normal. The pet should be fasted for 12 hours beforehand but must have access to water. Albumin should also be remeasured at the same time. If the repeated value for total calcium is still low, then doing an ionized calcium test is recommended since it is the definitive test for measuring calcium levels. In some situations, your veterinarian may advise that your pet have the ionized calcium test after finding a low total calcium.
"Once hypocalcemia is confirmed, the challenge is to identify the underlying cause."
Once hypocalcemia is confirmed, the challenge is to identify the underlying cause. Further testing will be needed to assess the health of the kidneys, the pancreas, the digestive system, and the parathyroid glands, as well as tests to look for evidence of antifreeze poisoning and nutritional problems. Hypocalcemia in a nursing female dog is easily diagnosed in the period just after whelping.
Why is measuring parathyroid hormone (PTH) important?
Since the parathyroid glands are responsible for controlling calcium levels, measuring parathyroid hormone (PTH) levels is the easiest way of determining if the parathyroid glands are working properly. If a pet has both hypocalcemia and low levels of parathyroid hormone, and there is no evidence of other disease, then primary hypoparathyroidism is the likely diagnosis. This is usually due to a poorly functioning parathyroid gland.
Can hypocalcemia be treated?
Yes. Primary hypoparathyroidism can be managed with a medication called calcitriol (brand names: Rocaltrol®, Calcijex®) plus nutritional supplements containing vitamin D and calcium. Hypocalcemia that develops secondary to other conditions usually resolves or improves once the underlying problem is treated.
