Calcium

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:

• 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 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.

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 Comprehensive Metabolic Panel and the Basic Metabolic Panel, two sets of tests often used in initial evaluation of a person or as part of routine health screening.

A doctor also may order a calcium test when someone has:

• 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 abdominal cramps, muscle cramps, or tingling fingers
• Other diseases that have been associated with abnormal blood calcium, such as thyroid disease, intestinal disease, 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, and 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 their side or back in the area of the kidneys, pain that may progress to lower in the abdomen, and/or blood in the urine.

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 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:

• 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 and causes the release of calcium from the bone 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

Urinary calcium levels may be affected by the same conditions and diseases that affect blood levels (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.

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.