Test Quick Guide

Calcium is the most abundant and one of the most important minerals in the body. It is essential for cell signaling and the proper functioning of muscles, nerves, and the heart. Calcium is needed for blood clotting and is crucial for the formation, density, and maintenance of bones and teeth. A calcium test measures the amount of calcium in the blood or urine, which reflects the amount of total and ionized calcium in the body.

About the Test

Purpose of the test

A blood calcium test screens for, diagnoses, and monitors a range of conditions relating to the bones, heart, nerves, kidneys, and teeth. The test may also be ordered if you have 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 performed together to diagnose or monitor various conditions.

When an abnormal total calcium result is obtained, it indicates an underlying problem. To help diagnose the issue, additional tests are often performed to measure ionized calcium, urine calcium, phosphorus, magnesium, vitamin D, parathyroid hormone (PTH), and PTH-related peptide (PTHrP). PTH and vitamin D maintain calcium concentrations in the blood within a narrow range of values.

If the blood 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. 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 their changes) is just as important as the concentrations.

Calcium can be used as a diagnostic test if you have symptoms that suggest:

  • Kidney stones
  • Bone disease
  • Parathyroid disorders
  • Neurologic disorders

Total calcium is the blood test most frequently ordered to evaluate calcium status. In most cases, it is a good reflection of the amount of free calcium in the blood since the balance between free and bound is usually stable and predictable.

However, in some people, the balance between free and bound 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.

Ionized calcium should be the test of choice for people who are critically ill, receiving blood transfusions or intravenous fluids, undergoing major surgery, and who have blood protein abnormalities like low albumin.

Large fluctuations in ionized calcium can cause: the heart to slow down or beat too rapidly, muscles to go into spasm (tetany), and confusion or even coma. In those who are critically ill, it can be extremely important to monitor the ionized calcium level to treat and prevent serious complications.

What does the test measure?

About 99% of calcium is found complexed in the bones, while the remaining 1% circulates in the blood. Calcium levels are tightly controlled; if there is too little absorbed or ingested or excess loss through the kidney or gut, calcium is taken from bone to maintain blood concentrations.

Roughly half of the calcium in the blood is “free” and metabolically active. The remaining half is “bound” to proteins, primarily albumin and to a lesser extent, globulins, with a smaller amount complexed to anions, such as phosphate. These bound and complex forms are metabolically inactive.

There are two tests to measure blood calcium. The total calcium test measures free and bound forms, while the ionized calcium test measures the free, metabolically active form.

Some calcium is lost daily, filtered from the blood by the kidneys, and excreted into the urine and sweat. Measurement of the amount of calcium in the urine is used to determine how much calcium the kidneys are eliminating.

When should I get this test?

A blood calcium test is often ordered when you undergo a general medical examination. It is typically included in the CMP and the 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 high or low calcium symptoms until their levels are very out of range. A health care practitioner may order a calcium test when you have:

  • 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 disorders, malabsorption, cancer, or malnutrition

An ionized calcium test may be ordered when you have numbness around the mouth, hands, and feet as well as muscle spasms in the same areas. These can be symptoms of low levels of ionized calcium. But when calcium levels fall slowly, many people have no symptoms at all.

Calcium monitoring may be necessary when you have certain kinds of cancer (particularly breast, lung, head and neck, kidney, or multiple myeloma), kidney disease, or 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.

A urine calcium test may be ordered when you have symptoms of kidney stones, such as a sharp pain in your side or back around the kidneys, pain that may progress to lower in the abdomen, and/or blood in the urine.

Finding a Calcium Test

How can I get a calcium test?

The standard calcium test uses a blood sample obtained with a blood draw at your doctor’s office, a hospital, or a laboratory.

Urine tests for calcium are also available. When needed, they are normally conducted by collecting all of the urine you produce over a full day so that the laboratory can measure the total amount of calcium you excreted during that time.

Blood and urine tests are normally done after being prescribed by a doctor or other health professional.

Can I take the test at home?

You can take a calcium test at-home, either with a blood or urine sample. If using a 24-hour urine test, you will need to collect your urine wherever you are during the day. For blood tests, you’ll need to visit a local laboratory to have your sample collected.

How much does the test cost?

The cost of a calcium test can change based on many factors, such as if calcium is measured alone or as part of a panel test and if it uses a blood or urine sample.

The final cost of a calcium test can involve several components, including office visits, technician fees for taking your sample, and/or charges for laboratory evaluation.

Your insurance company may pay for some or all of these costs if your calcium test is prescribed by your doctor. For the most definitive information about likely costs, talk with your doctor’s office and medical insurance company.

Taking a Calcium Test

Blood tests are the most common type of calcium test. A blood sample is taken in a medical lab, hospital, or doctor’s office for this test.

For a urine calcium test, you may provide a one-time sample at a medical office or lab, or you may be asked to do a 24-hour sample in which you collect all of the urine you produce over a day in special containers.

Before the test

If you are taking a calcium blood test, you may need to fast for eight to 12 hours beforehand. Check with your doctor whether you can eat and drink before the blood draw.

For a blood or urine test, you may need to temporarily stop taking certain medications beforehand to ensure the most accurate test results. Some prescription or over-the-counter drugs that affect mineral metabolism can affect calcium levels. These include lithium, antacids, diuretics, and vitamin D supplements, among others.

Urinary calcium results are more meaningful if the patient has been on a low calcium, neutral ash diet for three days prior to urine collection. Your doctor can tell you whether you need to adjust your normal medications or diet before your test.

During the test

For a calcium blood test, a blood sample will be taken from a vein in your arm. Most of the time, an elastic band called a tourniquet will be tied around your upper arm. This increases blood flow in your arm and makes it easier to access the vein.

The technician will use an antiseptic wipe on your skin near the vein and insert a needle. A vial of blood will be withdrawn, and then the needle will be taken out.

The total blood draw usually lasts only a few minutes. There may be some pain during the procedure, and many people feel a brief sting when the needle is inserted.

For a 24-hour urine sample, you will be given bags or containers for collecting your urine for a full day. You will need to have a container with you throughout the day so that you can collect urine regardless of where you are. Once you have finished the 24-hour collection, follow the instructions for bringing your sample to the lab.

After the test

After a calcium blood test, a cotton swab or bandage will be placed over the puncture site to stop any bleeding. You can return to most normal activities once the test is over. Slight pain or bruising can affect your arm but normally goes away quickly.

There are few or no lasting effects from calcium urine tests. Once you have provided a spot or a 24-hour urine sample, you can engage in daily activities without restrictions.

Calcium Test Results

Receiving test results

In most cases, results for both blood and urine calcium tests are available within a period of a few business days.

Test results can be sent by mail or accessible through online health portals. You may also receive a call or email from your doctor to either review your results or to schedule a follow-up appointment.

Interpreting test results

Blood calcium levels do not indicate levels of bone calcium but rather how much calcium is circulating in the blood.

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.

But because about half of the calcium in the 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 laboratory results, generally means that your calcium metabolism is normal and blood levels are being appropriately regulated.

Two of the more common causes of high blood calcium, called hypercalcemia, are:

  • Hyperparathyroidism, an increase in parathyroid gland function usually caused by a benign tumor of the parathyroid gland. This usually mild form of hypercalcemia can be present for many years before being noticed.
  • Cancer, which can cause hypercalcemia when it spreads to the bones and causes the release of calcium from the bone into the blood — or when cancer produces a hormone similar to PTH, resulting in increased calcium levels.

Some other causes of high blood calcium include:

  • Hyperthyroidism
  • Paget’s disease of bone
  • Sarcoidosis
  • Tuberculosis
  • Prolonged immobilization
  • Excess vitamin D intake
  • Thiazide diuretics
  • Kidney transplant
  • HIV/AIDS

The most common cause of low total calcium, called hypocalcemia, is:

  • Low blood protein levels, especially a low level of albumin, which can result from liver disease, malabsorption syndromes, or malnutrition. Also, low albumin is very common if you 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 low calcium 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

The reference ranges provided here represent a theoretical guideline that should not be used to interpret your test results. Some variation is likely between these numbers and the reference range reported by the lab that ran your test. Please consult your health care provider.

Urinary calcium levelsmay 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.

Asking questions can help you understand the meaning of your calcium test results. When you talk with your doctor, some of these questions may be helpful to review:

  • Was my calcium level low, normal, or high?
  • Were any other measurements taken along with calcium? If so, were they normal or abnormal?
  • If my calcium was too high or too low, what do you think is the most likely cause?
  • Are there any follow-up tests that you recommend?
  • Should I have another calcium test?
  • Should I make any changes to my diet?

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