To determine if the concentration of calcium in your blood is at normal levels.
A blood sample taken from a vein in your arm; a timed urine collection may be used when blood calcium concentration is abnormal; urine calcium measurements may also be requested if you have kidney stones
Current practice does not require fasting or any other test preparation.
Calcium is one of the most important minerals in the body. About 99% of it is found in the bones, and most of the rest circulates in the blood. Roughly half of the calcium is referred to as 'free' (or 'ionized'), and is active within the body; the remaining half, referred to as 'bound' calcium, is attached to protein and other compounds and is inactive.
Most commonly, doctors measure the total amount of calcium in the blood (called total calcium); this measures both the active and inactive forms of calcium. If measurement of the active form of calcium (ionized calcium) is needed, special sample handling is required. Urine calcium tells how much calcium is being excreted by the kidneys.
How is the sample collected for testing?
A blood sample is taken by needle from a vein in the arm. A urine specimen may be required if your blood calcium concentration is abnormal or if you have kidney stones, a timed collection is then preferred.
Is any test preparation needed to ensure the quality of the sample?
Current practice does not require fasting or any other test preparation. However, it is advisable that prolonged tourniquet use and fist clenching during collection of the blood sample should be avoided as this may affect the result generated by the laboratory.
How is it used?
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 e.g. 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.
When is it requested?
For Diagnosis: 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 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.
What does the test result mean?
A normal blood calcium result with other normal laboratory results suggests you have no problems with calcium metabolism (use by the body).
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.
Other causes of hypercalcaemia include:
- bone breaks combined with bed rest or not moving for a long periods of time
- excess Vitamin D intake
- kidney transplant
- 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.Low calcium can be 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 phosphate
- acute inflammation of the pancreas
- chronic kidney disease
- calcium ions becoming bound to protein (alkalosis)
- bone disease
- malnutrition, and
Causes of low 'free' calcium levels include all the above, except low protein levels.
Is there anything else I should know?
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.
Should I take a calcium supplement? A healthy diet should contain enough calcium, however some individuals do not take enough calcium in their diet and may consider a supplement. Calcium is particularly important in growing children, to maintain bone growth and in post-menopausal women who may develop low bone mass and be at risk of osteoporosis. It is important to discuss with your doctor the risks and benefits of starting a supplement.
Should I take a calcium supplement?
A healthy diet should contain enough calcium, however some individuals do not take enough calcium in their diet and may consider a supplement. Calcium is particularly important in growing children, to maintain bone growth and in post-menopausal women who may develop low bone mass and be at risk of osteoporosis. It is important to discuss with your doctor the risks and benefits of starting a supplement.
What foods are high in calcium?
Dairy products are the main source of calcium, but lesser amounts are found in eggs, fish, green leafy vegetables, broccoli, beans and pulses, nuts, and whole grains. Many fruit juices now have calcium added.
If I consume foods high in calcium, would it change my laboratory results?
In general, consuming such foods will not affect your calcium test results.
Can I perform this test at home?
No. While there are hand-held instruments available, these are intended for use in a hospital or GP surgery setting and must be operated by trained personnel.
On This Site
Tests: Phosphate, Vitamin D, Parathyroid Hormone (PTH), Albumin; Magnesium; Kidney Stone Analysis; Kidney Stone Risk Panel
Conditions: Kidney disease; Thyroid disease; Breast Cancer; Multiple Myeloma; Alcoholism