Also known as: Total calcium; Ionized calcium
Formal name: Calcium
Related tests: Phosphorus; Vitamin D; Parathyroid hormone (PTH); Magnesium; Albumin; Comprehensive metabolic panel (CMP); Basic metabolic panle (BMP)
Why Get Tested?
To determine if the level of calcium in your blood is within normal limits.
When to Get Tested?
As part of a routine metabolic panel, when you have a kidney, bone, or nerve disease, or when symptoms of significantly increased or decreased calcium concentrations are present.
A blood sample drawn from a vein in your arm; sometimes a timed urine collection such as a 24-hour urine sample.
Test Preparation Needed?
Current practices do not require fasting or any other test preparation.
The Test Sample
What is being tested?
This test measures the amount of calcium in the blood or urine. Calcium is one of the most important minerals in the body. It is essential for the proper functioning of muscles, nerves, and the heart and is required in blood clotting and in the formation of bones. About 99% of calcium is found in the bones while the remaining 1% circulates in the blood. Roughly half of the calcium in the blood is "free" and is metabolically active. The remaining half is "bound" to albumin and other compounds and is metabolically inactive.
There are two tests to measure blood calcium. The total calcium test measures both the free and bound forms. The ionized calcium test measures only the free, metabolically active form.
Some calcium is lost from the body every day, filtered from the blood by the kidneys and excreted into the urine. Measurement of the amount of calcium in the urine is used to determine how much calcium is being eliminated by the kidneys.
How is the sample collected for testing?
A blood sample is taken by needle from a vein in the arm. If a urine collection is required, a 24-hour urine sample or a timed collection is obtained.
Is any test preparation needed to ensure the quality of the sample?
Current practices do not require fasting or any other test preparation
How is it used?
A blood calcium test is ordered to screen for, diagnose, and monitor a range of conditions relating to the bones, heart, nerves, kidneys, and teeth. Blood calcium levels do not directly tell how much calcium is in the bones, but rather, how much calcium is circulating in the blood.
A total calcium level is often measured as part of a routine health screening. It is included in the comprehensive metabolic panel (CMP) and the basic metabolic panel (BMP) – groups of tests that are performed together to diagnose or monitor a variety of conditions. When an abnormal total calcium result is obtained, it is viewed as an indicator of an underlying problem. To help diagnose the underlying problem, additional tests are often done to measure ionized calcium, urine calcium, phosphorous, magnesium, vitamin D, and parathyroid hormone (PTH). PTH and vitamin D are responsible for maintaining calcium concentrations in the blood within a narrow range of values.
Measuring calcium and PTH together can help determine whether the parathyroid glands are functioning normally. Measuring urine calcium can help determine whether the kidneys are excreting the proper amount of calcium, and testing for vitamin D, phosphorus, and/or magnesium can help determine whether other deficiencies or excesses exist. Frequently the balance among these different substances, and the changes in them, are just as important as the concentrations.
Calcium can be used as a diagnostic test if a person has symptoms that suggest:
The total calcium test is the test most frequently ordered to evaluate calcium status. In most cases, it is a good reflection of the amount of free calcium present in the blood since the balance between free and bound is usually stable and predictable. However, in some people, the balance between bound and free calcium is disturbed and total calcium is not a good reflection of calcium status. In these circumstances, the measurement of ionized calcium may be necessary. Some conditions where ionized calcium should be the test of choice include: critically ill patients who are receiving blood transfusions or intravenous fluids, patients undergoing major surgery, and patients with blood protein abnormalities like low albumin.
Large fluctuations in ionized 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. In those who are critically ill it can be extremely important to monitor the ionized calcium level, in order to be able to treat and prevent serious complications.
When is it ordered?
A blood calcium level is often ordered as a screening test when a person undergoes a general medical examination. It is typically included in the CMP and the BMP – two sets of tests often used in initial evaluation of a person or as part of routine health screening.
The doctor also may order a calcium test when someone has:
An ionized calcium test may be ordered when someone has numbness around the mouth and in the hands and feet and muscle spasms in the same areas. These can be symptoms of low levels of ionized calcium. However, when calcium levels fall slowly, many people have no symptoms at all.
Calcium monitoring may be necessary when a person has certain kinds of cancer (particularly breast, lung, head and neck, kidney, and multiple myeloma), has kidney disease, or has had a kidney transplant. Monitoring may also be necessary when someone is being treated for an abnormal calcium level, to evaluate the effectiveness of treatments such as calcium or vitamin D supplements.
A urine calcium test may be ordered when someone has symptoms of kidney stones such as a sharp pain in side or back in the area of the kidneys, pain that may progress to lower in the abdomen and/or blood in the urine.
What does the test result mean?
Calcium absorption, use, and excretion are regulated and stabilized by a feedback loop involving PTH and vitamin D. Conditions and diseases that disrupt calcium regulation can cause inappropriate acute or chronic elevations or decreases in calcium and lead to symptoms of hypercalcemia or hypocalcemia.
In most cases, total calcium is measured because the test is more easily performed than the ionized calcium test and requires no special handling of the blood sample. Total calcium is usually a good reflection of free calcium since the free and bound forms are typically each about half of the total. However, because about half the calcium in blood is bound to protein, total calcium test results can be affected by high or low levels of protein. In such cases, it is more useful to measure free calcium directly using an ionized calcium test.
A normal total or ionized calcium result together with other normal lab results generally means that a person’s calcium metabolism is normal and blood levels are being appropriately regulated.
High Total Calcium - Hypercalcemia
Two of the more common causes of hypercalcemia are:
Some other causes of hypercalcemia include:
Instructions for Hypercalcemia
You have been diagnosed with hypercalcemia. That means you have too much calcium in your blood. Calcium is a mineral that helps develop bones and teeth, controls heart rhythm, and allows muscles to contract. Hypercalcemia is often the result of problems elsewhere in the body, including overactive glands, unhealthy bones, long-term bed rest, and certain tumors or cancers.
Follow up with your healthcare provider, or as advised.
When to call your healthcare provider
Call your healthcare provider right away if you have any of the following:
Low Total Calcium – Hypocalcemia
The most common cause of low total calcium is:
Low blood protein levels, especially a low level of albumin. In this condition, only the bound calcium is low. Ionized calcium remains normal and calcium metabolism is being regulated appropriately.
Some other causes of hypocalcemia include:
Urinary calcium level may be affected by the same conditions and diseases that affect the blood level (listed above). In cases of suspected kidney stones, the cause may be due a high level of calcium in the urine. Hypercalciuria is an inherited disordered that can lead to kidney stones. Hypercalcuria causes increased calcium in the urine which leads to the formation of crystals in the kidneys and other parts of the urinary tract. It may be the cause of kidney stones in about half of affected people.
Hypocalcemia can cause the muscles of the face, hands, and feet to twitch without your control (spasm). It can also cause numbness or tingling around your mouth or in your hands and feet. Other problems may include depression and memory loss.
A blood sample will be taken to check your calcium level. The test also helps figure out if hypocalcemia may be caused by a problem with your kidneys, or with the gland that controls your calcium level (parathyroid gland). Depending on the cause, you may be given an oral calcium supplement. In severe cases, you may need a shot (injection) of calcium gluconate. You may also have a vitamin D shot or supplement. If low magnesium is the cause, you will have treatment to raise your body’s level of this mineral.
Follow up as advised by your healthcare provider, or as advised.
When to seek medical advice
Call your healthcare provider right away if any of these occur:
Is there anything else I should know?
Newborns, especially premature and low birthweight infants, often are monitored during the first few days of life for neonatal hypocalcemia, using the test for ionized calcium. 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 supplemental calcium, given orally or intravenously.
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 used for this purpose.
Taking thiazide diuretic drugs is the most common drug-induced reason for a high calcium level
Should I be concerned if my doctor only orders a regular calcium and not free or ionized calcium?
No. Measuring total calcium is usually sufficient for screening purposes. The total calcium test is more easily performed than the ionized calcium test since it requires no special handling of the blood sample. The ionized calcium test, on the other hand, requires specialized handling and expedited delivery of the blood sample to the lab for prompt analysis. The necessary handling and delivery is difficult to achieve outside of a hospital setting. In most cases, total calcium is a good substitute for free calcium since the free and bound forms are usually each about half of the total. The direct measurement of ionized calcium is particularly important during surgery as well in severely ill patients, when changes in total calcium do not reliably tell how abnormal the ionized calcium level is.
What foods are high in calcium?
Dairy products are the main source of calcium, but lesser amounts are found in eggs, green leafy vegetables, broccoli, legumes, nuts, and whole grains. Many fruit juices are now fortified with calcium.
If I consume foods fortified with calcium, would it change my laboratory results?
In general, consuming fortified foods will not directly affect your calcium test results. Talk to your doctor about your calcium requirements. He can help you determine whether you should be taking calcium and/or vitamin supplements.
Can I perform this test at home?
No. While there are hand-held instruments available, these are intended for use in a hospital or medical office setting and must be operated by trained personnel.
Disclaimer: The UCLA Health System cannot guarantee the accuracy of such information. The information is provided without warranty or guarantee of any kind. Please speak to your Physician before making any changes.