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. The test may also be ordered if a person has symptoms of a parathyroid disorder, malabsorption, or an overactive thyroid.
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, parathyroid hormone (PTH) and PTH-related peptide (PTHrP). PTH and vitamin D are responsible for maintaining calcium concentrations in the blood within a narrow range of values.
If the calcium is abnormal, 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) is 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, those who are receiving blood transfusions or intravenous fluids, patients undergoing major surgery, and people 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 test is often ordered when a person undergoes a general medical examination. It is typically included in the comprehensive metabolic panel (CMP) and the basic metabolic panel (BMP), two sets of tests that may be used during an initial evaluation or as part of a routine health screening.
Many people do not have symptoms of high or low calcium until their levels are very out of range. A health practitioner may order a calcium test when someone has:
Kidney disease, because low calcium is especially common in those with kidney failure
Symptoms of high calcium such as fatigue, weakness, loss of appetite, nausea, vomiting, constipation, abdominal pain, urinary frequency, and increased thirst
Symptoms of very low calcium such as abdominal cramps, muscle cramps, or tingling fingers
Other diseases that have been associated with abnormal blood calcium such as thyroid disease, parathyroid disorder, malabsorption, cancer, or malnutrition
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, or multiple myeloma), has kidney disease, or has had a kidney transplant. Monitoring may also be necessary when someone is being treated for abnormal calcium levels 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 the person’s side or back around the kidneys, pain that may progress to lower in the abdomen, and/or blood in the urine.
Some other causes of hypercalcemia include:
Excess vitamin D intake
Low total calcium (hypocalcemia)
The most common cause of low total calcium is:
Low blood protein levels, especially a low level of albumin, which can result from liver disease or malnutrition, both of which may result from alcoholism or other illnesses. Low albumin is also very common in people who are acutely ill. With low albumin, 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
Increased levels of phosphorus
Acute inflammation of the pancreas (pancreatitis)
Urinary calcium levels may be affected by the same conditions and diseases that affect blood levels (listed above). A high level of calcium in the urine (hypercalciuria) may lead to the formation of crystals or calculi (stones) in the kidneys. About 75% of kidney stones contain calcium.