How is it used?
Blood calcium is tested 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 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 or some kind of 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 gland is 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 you go to your doctor with symptoms that suggest:
Kidney stones
Bone disease
Neurologic disorders
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 involved in metabolism since the balance between free and bound is usually stable and predictable. However, in some patients, the balance between bound and free calcium is disturbed and total calcium is not a good reflection of calcium status. In those circumstances, measurement of ionized calcium is necessary. Some conditions where ionized calcium should be the test of choice include: critically ill patients who are receiving transfusions or IV 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 critically ill patients, it is extremely important to know the ionized calcium level to be able to intervene and prevent serious complications.
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When is it ordered?
Calcium is often ordered as a screening test when you undergo a general medical examination. It is typically included in the
Comprehensive Metabolic Panel and the
Basic Metabolic Panel two sets of tests often used in initial evaluation of a patient or as part of health screening.
Your doctor also may order a calcium test when you have:
Kidney disease, because low calcium is especially common in those with kidney failure;
Symptoms of too much calcium, such as fatigue, weakness, loss of appetite, nausea, vomiting, constipation, abdominal pain, urinary frequency, and increased thirst;
Symptoms of low calcium, such as cramps in your abdomen, muscle cramps, or tingling fingers; or
Other diseases that have been associated with abnormal blood calcium, such as thyroid disease, intestinal disease, cancer, or poor nutrition.
Your doctor may order an ionized calcium test when you have 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.
You may need calcium monitoring when you have certain kinds of cancer (particularly breast, lung, head and neck, kidney, and multiple myeloma), have kidney disease, or have had a kidney transplant. Monitoring may also be necessary when you are being treated for abnormal calcium levels to evaluate the effectiveness of treatments such as calcium or vitamin D supplements.
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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.
Normal calcium
A normal total or ionized calcium result together with other normal lab results generally means that your calcium metabolism is normal and blood levels are being appropriately regulated.
High Total Calcium - Hypercalcemia
Two of the more common causes of hypercalcemia are:
Hyperparathyroidism, an increase in parathyroid gland function: This condition is usually caused by a benign tumor of 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 a cancer produces a hormone similar to PTH, resulting in increased calcium levels.
Some other causes of hypercalcemia include:
Hyperthyroidism
Sarcoidosis
Tuberculosis
Prolonged immobilization
Excess Vitamin D intake
Kidney transplant
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:
Underactive parathyroid gland (hypoparathyroidism)
Inherited resistance to the effects of parathyroid hormone
Extreme deficiency in dietary calcium
Decreased levels of vitamin D
Magnesium deficiency
Increased levels of phosphorus
Acute inflammation of the pancreas (pancreatitis)
Renal failure
Malnutrition
Alcoholism
NOTE: The result of your total calcium test is measured by your doctor against a reference range for the test to determine whether the result is “normal” (it is within the range of numbers), high (it is above the high end of the range), or low (it is below the low end of the range). Because there can be many variables that affect the determination of the reference range, the reference range for this test is specific to the lab where your test sample is analyzed. For this reason, the lab is required to report your results with an accompanying reference range. Typically, your doctor will have sufficient familiarity with the lab and your medical history to interpret the results appropriately
While there is no such thing as a “standard” reference range for total calcium, most labs will report a similar, though maybe not exactly the same, set of numbers as that included in medical textbooks or found elsewhere online. For this reason, we recommend that you talk with your doctor about your lab results. For general guidance only, we are providing the below from the classic medical text, Tietz Textbook of Clinical Chemistry and Molecular Diagnostics.
For more information on reference ranges, please read Reference Ranges and What They Mean.
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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.
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