If someone was asked about the importance of calcium in the body, most people would associate it with a strong, healthy skeletal system. While this is true, calcium is important for much more than that. It is extremely important for the normal functioning of the neurologic and muscular systems as well. A normal calcium level is so important to the functioning of the body that there is a complex system in place to keep the blood calcium level in a very specific range.
In dogs, low blood calcium levels are occasionally seen associated with small dogs that are nursing young puppies. The loss of calcium though milk production can cause a low blood calcium level before the body can respond to increase this calcium level back to normal. More commonly, dogs are seen with an increased blood calcium level, otherwise known as hypercalcemia. This condition can occur for a variety of reasons.
Occasionally a high blood calcium level may be found when just routine blood work is done as part of a wellness profile. If there are no other abnormalities on examination or on the blood work and the calcium increase is mild, it may be appropriate to just recheck it another day to see if it is persistently high or if it was just a transient increase.
An elevated blood calcium level on an ill dog must always be considered significant. Clinical signs specifically related to a high blood calcium level include an increase in drinking, an increase in urination, lethargy, decrease in appetite, and weakness. If the increased blood calcium gets severe enough there can be an effect on the heart as well, leading to arrhythmias.
Kidney failure is one potential cause of increased blood calcium levels. If this is the cause, there are normally other findings on the blood work indicating that kidney failure is the primary problem. The kidneys play an important role in maintaining a normal blood calcium level. When they aren’t functioning normally, the blood calcium level may rise to levels so that clinical signs are seen.
Another cause of high blood calcium levels is Primary Hyperparathyroidism. In dogs there are two thyroid glands in the neck and on those thyroid glands are smaller glands called parathyroid glands. With Primary Hyperparathyroidism one or more of these parathyroid glands produce too much parathyroid hormone. This hormone is important in keeping the blood calcium level in the normal range. Too much of this hormone can cause the blood calcium level to increase. Typically the increase in the calcium level seen with this condition is fairly mild and less likely to cause clinical signs.
There is a syndrome associated with high blood calcium levels called the Hypercalcemia of Malignancy. There are several types of malignant tumors that have been associated with high blood calcium levels, including lymphoma, anal gland carcinomas, and mammary gland carcinomas. These tumors can secrete several substances, including parathyroid hormone, which will cause an increase in the blood calcium by releasing it from bones and causing it to be reabsorbed in the kidneys instead of being urinated out of the body.
Lastly, Addison’s Disease (Hypoadrenocorticism) can cause an increase in blood calcium levels. This is a condition where the adrenal glands don’t produce enough corticosteroids for normal body function. Although there can be an increase in blood calcium levels, usually the dog will get very ill from the low corticosteroid level way before there will be clinical signs from the high calcium levels.
Clinical signs from an elevated blood calcium level can go from mild to life threatening very quickly. If your dog starts showing any of the clinical signs mentioned earlier, get your dog to your veterinarian as soon as possible for evaluation. An even better option for dogs, especially as they get to their geriatric years, is to have your veterinarian run annual blood work to check for many conditions commonly seen in older dogs. This could possibly diagnose problems in your dog before it would ever get to the life threatening condition of hypercalcemia.
Chad Higgins, DVM, is a 1989 graduate of Purdue University School of Veterinary Medicine. He has owned Amanda Animal Hospital in Spencerville for almost 17 years and sees dogs, cats, and other furry little critters.