Serum Calcium (Ca)

Calcium is often used as a screening test as part of a general medical examination. It is typically included in the comprehensive metabolic panel.

Calcium can be used as a diagnostic test if you go to your doctor with symptoms that suggest:

  • kidney stones,
  • bone disease, or
  • neurologic (nerve-related) disorders.

Your doctor also may order 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 fatigue, 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.

Your doctor may order an ionized calcium test if you have numbness around the mouth and in the hands and feet and muscle spasms in the same areas, which are symptoms of low levels of ionized calcium. If calcium levels fall slowly, however, many people have no symptoms at all.

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

A normal calcium result with other normal lab results means that 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), these two tests are usually ordered together. Calcium values must be interpreted in combination with albumin to determine if the calcium concentration of serum is appropriate. As albumin levels rise, calcium rises as well, and vice versa.

A high calcium level is called hypercalcemia. You have too much calcium in your blood and will need treatment for the underlying condition. This usually is caused by:

  • Hyperparathyroidism (increase in parathyroid gland function): This condition is usually caused by a benign (not cancerous) tumor on the parathyroid gland. This form of hypercalcemia is usually mild and can be present for many years before being noticed.
  • Cancer: Cancer can cause hypercalcemia 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.

Other causes of hypercalcemia include:

  • hyperthyroidism,
  • sarcoidosis,
  • tuberculosis,
  • bone breaks combined with bed rest or not moving for a long periods of time,
  • excess Vitamin D intake,
  • kidney transplant, and high protein levels (for example, if a tourniquet is used for too long while blood is collected). In this case, free or ionized calcium remains normal.

High levels of ionized calcium occur with all the above, except high protein levels.

Low calcium levels, called hypocalcemia, mean that you do not have enough calcium in your blood or that you don’t have enough protein 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 ionized calcium level remains normal.

Low calcium, known as hypocalcemia, is caused by many conditions:

  • low protein levels,
  • underactive parathyroid gland (hypoparathyroidism),
  • decreased dietary intake of calcium,
  • decreased levels of vitamin D,
  • magnesium deficiency,
  • too much phosphorus,
  • acute inflammation of the pancreas,
  • chronic renal failure,
  • calcium ions becoming bound to protein (alkalosis),
  • bone disease,
  • malnutrition, and alcoholism.

Causes of low ionized calcium levels include all the above, except low protein levels.

Calcium Regulation

Calcium Regulation

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