Blood calcium is tested to help diagnosis, and to monitor a range of conditions relating to the bones, heart, nerves and kidneys. Doctors can get a better understanding of your health by comparing your calcium result and your phosphate result at the same time. For example, when parathyroid hormone (PTH) from the parathyroid gland is released, calcium levels rise and phosphate falls. However in kidney disease, high phosphate levels and low calcium levels are often seen. Depending on the levels you have, these two tests can help your doctor discover whether you have a parathyroid disorder or other conditions.
Directly measuring 'free' calcium can be valuable in certain situations where the total calcium level is likely to be misleading eg during major surgery (particularly after a blood transfusion), in critically ill patients, and when protein levels are very abnormal. Large fluctuations in free calcium can cause the heart to slow down or to beat too rapidly, can cause muscles to go into spasm (tetany), and can cause confusion or even coma.
For Screening: Calcium is often used as a screening test in a general medical examination.
For Diagnosis:Calcium can be used as a diagnostic test if you go to your doctor with symptoms that suggest:
bone disease, or
neurologic (nerve-related) disorders.
Your doctor also may request a calcium test if:
you have kidney disease, because low calcium is especially common in those with kidney failure;
you have symptoms of too much calcium, such as tiredness, weakness, loss of appetite, nausea, vomiting, constipation, abdominal pain, urinary frequency, and increased thirst;
you have symptoms of low calcium, such as cramps in your abdomen, muscle cramps, or tingling fingers; or
you have other diseases that can be associated with abnormal blood calcium, such as thyroid disease, intestinal disease, cancer, or poor nutrition.
If calcium levels fall slowly, however, many people have no symptoms at all.
For Monitoring: You may need calcium monitoring as part of your regular laboratory tests if you have certain kinds of cancer (particularly breast, lung, head and neck, kidney, and multiple myeloma) or kidney disease or transplant. You may need to be monitored for calcium level also if it is clear that you have abnormal calcium levels or if you are receiving calcium or vitamin D supplements.
A normal blood calcium result with other normal lab results suggests you have no problems with calcium metabolism (use by the body).
Because about half of the calcium in your blood is bound by albumin (a protein), your doctor must take into account the albumin level in your blood when interpreting the calcium result.
A high calcium level is called hypercalcaemia. This means you have too much calcium in your blood and will need treatment for the condition that is causing this. This is usually:
Hyperparathyroidism (increase in parathyroid gland function): This condition is usually caused by a benign (not cancerous) tumour on the parathyroid gland. This form of hypercalcaemia is usually mild and can be present for many years before being noticed.
Cancer: Cancer can cause hypercalcaemia when it spreads to the bones, which releases calcium into the blood, or when cancer causes a hormone similar to PTH to increase calcium levels.
some drugs used to increase water excretion (diuretics), and
high protein levels. In this case the 'free' calcium remains normal.
High levels of 'free' calcium occur with all the above, except high protein levels.
Low calcium levels, called hypocalcaemia, mean that you do not have enough calcium in your blood. The most common cause of low total calcium is low protein levels, especially low albumin. When low protein is the problem, the 'free' calcium level remains normal.
Two hormones control blood calcium within a small range of values. Parathyroid hormone (PTH) is produced by a group of small glands in the neck (near the thyroid gland), stimulated by a decrease in 'free' calcium. PTH causes the release of calcium from bone and decreases calcium losses from the kidneys, so that calcium levels rise. PTH also stimulates production of activated Vitamin D by the kidneys.
Vitamin D, in turn, increases calcium absorption in the intestine, but decreases calcium lost from the kidneys in urine. It also decreases the production of PTH. Overall, as Vitamin D levels rise, calcium levels rise and PTH falls. In healthy people, these two hormones keep blood calcium at normal levels, even though maintaining that balance in the blood may cause calcium to be released from bones.
Newborns, especially premature and low birthweight infants, often are monitored during the first few days of life for neonatal hypocalcaemia. This can occur because of an immature parathyroid gland and doesn’t always cause symptoms. The condition may resolve itself or may require treatment with calcium given orally or by injection.
Blood and urine calcium measurements cannot tell how much calcium is in the bones. A test similar to an X-ray, called a bone density or 'Dexa' scan, is needed for this purpose.
Taking thiazide diuretic drugs (drugs that encourage urination) is the most common drug-induced reason for a high calcium level.
This article was last reviewed on 4 November 2007. | This article was last modified on 24 September 2013.
The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.
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