What A High Calcium Count Indicates

According to the Linus Pauling Institute at Oregon State University, calcium is the most abundant mineral in your body. Ninety-nine percent of your calcium stores are sequestered within your bones and teeth, while the remaining 1 percent is intimately involved in the day-to-day metabolic function of your other cells, tissues and organs. Calcium concentrations in your bodily fluids are normally tightly controlled to permit normal physiologic function. Elevated serum calcium, or hypercalcemia, can result from a variety of causes.

Regulation

Serum calcium levels are regulated through a complex mechanism involving vitamin D and your parathyroid glands, kidneys, intestine and bone. Whenever your calcium level falls, your parathyroid glands release parathyroid hormone, or PTH, which increases the activation of vitamin D in your kidneys and stimulates the release of calcium from your bones. Activated vitamin D enhances intestinal absorption of calcium, the reabsorption of calcium from your urine and -- in concert with PTH -- calcium release from your bones. As these actions raise your blood calcium level once again, PTH production ceases.

Immobilization

Any process that alters bone metabolism can increase your calcium levels. During prolonged periods of bed rest, such as during an illness or following an injury, your body tends to break down bone that is not being stressed by weight bearing. As calcium is removed from your skeleton, your serum calcium levels increase until the excess is eliminated through your kidneys. In the long run, this can result in weaker bones and increase your risk for osteoporosis.

Hormonal

Since PTH is designed to increase your serum calcium concentration, overproduction of PTH can cause an abnormally high calcium level. "The Merck Manual of Diagnosis and Therapy" states that over-secretion of PTH, a condition called hyperparathyroidism, is probably the most common cause of hypercalcemia. Hyperparathyroidism often results from benign PTH-secreting tumors in your parathyroid glands. Similarly, hyperthyroidism -- an overactive thyroid gland -- can accelerate bone turnover and contribute to abnormally high calcium levels.

Cancer

Several cancers, including lymphomas, multiple myeloma, leukemias and many carcinomas, can trigger elevated calcium levels. This is often the result of direct invasion of your bones by malignant cells, but cancers can cause hypercalcemia even when they haven't spread to your skeleton. The October 2010 issue of "Journal of Medical Case Reports" described a case of hypercalcemia caused by a malignant lymphoma that produced a compound called parathyroid hormone-like protein. This protein, which mimics the effects of PTH, has been identified in many cancer patients with hypercalcemia.

Considerations

Calcium levels are normally maintained within a fairly narrow range to permit optimal physiologic function. A calcium level above 10.4 mg/dL indicates hypercalcemia. Many conditions can cause hypercalcemia, including immobilization, thyroid or parathyroid disease, vitamin D toxicity, cancer, Paget's disease or even some medications, such as lithium, theophylline or thiazide diuretics. A high calcium level merits a thorough medical evaluation to determine its cause.