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How the body maintains a normal calcium level and avoids hypercalcaemia
The body maintains a normal calcium level by balancing the amount of calcium released from bone, the amount of calcium needed to rebuild new bone, the amount absorbed from the gastrointestinal tract, and the amount filtered out by the kidneys as waste (4).
Causes of hypercalcaemia
Hypercalcaemia means too much calcium in the blood. One of the causes of hypercalcaemia is an increased amount of calcium being released from bone, as occurs in bone metastases (3, 4). More calcium can be released by bone metastases than the kidney is capable of excreting (getting rid of) (3, 4). Another cause of hypercalcaemia is that the kidneys are not functioning correctly and are unable to filter enough calcium to lower blood levels to normal (3,4). Finally, a third cause of hypercalcaemia is an increased absorption of calcium from the gastrointestinal tract (this is a rare cause) (4).
Hypercalcaemia & Normal calcium metabolism
How common is hypercalcaemia in people with cancer?
Hypercalcaemia is not uncommon in people with cancer; 10% to 20% have hypercalcaemia (1, 2). The excess blood calcium is from the breakdown of bone by cancer (2). Hormones released by the tumor cells cause bone reabsorption by special cells called osteoclasts (4). Bone metastases release chemicals around their area to stimulate osteoclasts to re-absorb bone (4).
Symptoms of hypercalcaemia
The symptoms of hypercalcaemia may be vague and nonspecific (4). They are often confused with symptoms from the underlying tumor (4). Gastrointestinal symptoms included nausea, vomiting, and loss of appetite (3, 4). The nausea and vomiting can lead to dehydration (not enough water in the body), making the hypercalcaemia more severe (4). Neurologic symptoms include depression and fatigue (tiredness) (4). Other symptoms include itching and bone pain (4)
If you have any of these symptoms, you should ask your doctor to check the level of calcium in your blood.
Treatment of hypercalcaemia
The treatment for hypercalcaemia depends on its severity (3, 4). Mild hypercalcaemia, in which the level of calcium is only slightly elevated, may need no treatment (4). Moderate-to-severe hypercalcaemia needs to be treated (4). Intravenous fluids are given to combat dehydration (4). Bisphosphonates are synthetic (man-made) compounds similar to a naturally occurring chemical that is part of normal bone (1). Bisphosphonates bind strongly to bone (1). They are more resistant than the natural chemical to being broken apart by osteoclasts, so they prevent the osteoclasts from breaking down bone (1). Decreasing bone reabsorption decreases the serum calcium. Bisphosphonates are the most widely used treatment for hypercalcaemia (2). Another treatment for hypercalcaemia is a hormone that is normally secreted in the body, called calcitonin (2). Normally, calcitonin decreases the reabsorption of calcium from bone; calcitonin therapy gives extra calcitonin to combat bone breakdown (2). It lowers the serum calcium by decreasing the amount of calcium contributed from the bone. Unfortunately, with time, the effects of extra calcitonin decrease, so it is useful only as short-term therapy for hypercalcaemia (2). Finally, treating the tumor to decrease its size also decreases the chemicals that the tumor secretes to stimulate osteoclasts to re-absorb bone (4).
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References:
- "How ZOMETA® Works" http://www.us.ZOMETA.com/info/about/howitworks.jsp. Accessed 09/05/2003.
- Hypercalcaemia: Health Professional Version. http://cancer.gov/cancerinfo/pdq/supportivecare/hypercalcaemia/healthprofessional/. Accessed 09/06/2003.
- Hypercalcaemia: Patient Version. http://cancer.gov/cancerinfo/pdq/supportivecare/hypercalcaemia/patient/. Accessed 09/06/2003
- Morton AR, Lipton A. Hypercalcaemia. In: Abeloff MD, Armitage JO, Lichter AS, Niederhuber JE, eds. Clinical Oncology. 2nd Edition. Churchill Livingstone. 2000. pp 719-735.
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