What causes high blood calcium levels?

Calcium is an element that is important for the function of nearly every cell in the body. The levels of calcium in the blood (serum calcium) must be maintained within a specific range. When levels are too high, many problems can occur such as kidney stones, muscle weakness, abdominal pains, mood disturbances, fatigue and even cardiac arrhythmias.

There are many conditions which may cause high calcium levels. The most common cause of elevated calcium in the general, non-hospitalized population is hyperparathyroidism. The parathyroid glands are 4 small, pea sized glands located in the neck that make parathyroid hormone when the blood calcium levels are low. Parathyroid hormone increases the amount of calcium absorbed from food, increases the amount of calcium reabsorbed back into the body by the kidneys, and releases calcium from bones. When the calcium levels have been raised back to normal levels, the parathyroid glands should stop making and releasing parathyroid hormone. Occasionally, one or more of the parathyroid gland becomes diseased and doesn’t stop making parathyroid hormone. The parathyroid hormone level increases and the calcium level increases. This is called hyperparathyroidism. Usually this is due to the development of a benign (non-cancerous) tumor on one of the parathyroid glands. Very rarely, this could be due to parathyroid cancer.

There are many other causes of high calcium levels. Some types of cancer can cause elevated calcium levels. Tumors may increase calcium by making a hormone that is very similar to and functions like parathyroid hormone or they may increase calcium by causing the breakdown of muscle and bones, releasing calcium into the blood stream. Other cause of increased calcium level include: kidney disease, excess vitamin D consumption, diseases of bone and diseases of excess muscle breakdown (myopathies).

Because there are so many causes of high calcium levels and many health consequences of elevated calcium, all people who have a calcium blood test showing an abnormally high level need to have a full examination by a physician to rule out each of these causes.