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(Total Calcium; Ionized Calcium; Ca)

What Is Calcium?

Calcium is a mineral found in the body. It is used to build bones and help keep them strong. It helps the muscles, nerves, and heart work. It also helps the blood clot. Almost all calcium in the body is found in the bones. The rest is in the blood that flows through your body.

There are two forms of calcium. About half of it is free (ionized). The other half is bound to proteins. Examples are calcium phosphate and calcium citrate.

Reason for the Test

A calcium test may be ordered when a condition associated with abnormal calcium levels is suspected, such as a condition that affects the parathyroid gland or vitamin D levels. It may also be ordered to monitor blood levels of calcium if you have kidney, bone, heart, thyroid, or nerve diseases. It may also be a part of routine blood tests.

Type of Sample Taken

A blood sample is taken from an arm or hand.

Prior to Collecting the Sample

Your care team will tell you what to do before the test. You may need to stop taking some medicines, such as:

  • Antacids
  • Some vitamins
  • Thyroid medicine
  • Medicine to treat manic depression

People who drink a lot of milk may need to stop.

During the Sample Collection

You will be asked to sit. An area inside your elbow will be cleaned with a wipe. A large band will be tied around your arm. The needle will be put in a vein. A tube will collect the blood from the needle. The band on your arm will be taken off. After the blood is collected, the needle will be removed. Gauze will be held on the site to help stop bleeding. You may also be given a bandage. This test takes about 5-10 minutes.

After Collecting the Sample

After the sample is taken, you may need to sit for 10-15 minutes. If you are lightheaded, you may need to stay longer. When you feel better, you can leave.

In some people, a bit of blood may ooze from the vein below the skin and cause a bruise. You can help prevent bruising by putting pressure over the site. Any bruise will go away in a day or two.

After the sample has been taken, these problems may rarely happen:

  • Redness
  • Swelling
  • Persistent bleeding or discharge
  • Pain

Call your doctor right away if you have any of these problems.


It may take a few days to get your test results.

Adults8-10.5 mg/dL (2.2-2.6 mmol/L)
Children8.8-11.3 mg/dL (2-2.7 mmol/L)
Babies younger than one week7.6-12 mg/dL (1.8-3 mmol/L)

mg/dL=milligrams per deciliter

mmol/L=millimoles per liter

People with calcium that is too high may have health problems, such as:

  • Hyperparathyroidism
  • Cancer that has spread to the bones
  • Multiple myeloma
  • Side effects from medicine, such as taking too much vitamin D
  • Osteoporosis
  • Sarcoidosis
  • Milk alkali syndrome
  • Infections
  • Endocrine problems, such as Addison disease or thyrotoxicosis
  • Paget disease
  • Inherited abnormality of certain cells of the immune system

People with calcium that is too low may have health problems, such as:

  • Hypoparathyroidism
  • Chronic kidney disease
  • Liver disease
  • Rickets and osteomalacia
  • Malabsorption syndromes
  • Pancreatitis
  • Magnesium deficiency
  • Vitamin D or calcium deficiency
  • Poor calcium, phosphorus, and vitamin D intake
  • Low albumin

When ionized calcium is being measured, levels of 4.4 to 5.5 mg/dL (1.1 to 1.3 mmol/L) are considered normal.

Ionized calcium levels that are too high can be a sign of:

  • Hyperparathyroidism
  • Acidosis—body fluids that have too much acid
  • Too much vitamin D

Ionized calcium levels that are too low can be a sign of:

Many factors can affect the reliability of lab tests. A test may suggest an illness that actually does not exist. This is called a false positive. A test may also miss an illness that actually does exist. This is called a false negative.

A doctor will consider the results from many tests and your symptoms before making a diagnosis. It is important to discuss these results with your doctor before coming to any conclusions.


Calcium. Lab Tests Online—American Association for Clinical Chemistry website. Available at: https://labtestsonline.org/tests/calcium. Updated December 19, 2018. Accessed March 6, 2019.

Calcium and osteoporosis. EBSCO Nursing Reference Center website. Available at:https://www.ebscohost.com/nursing/products/nursing-reference-center. Updated October 19, 2018. Accessed March 7, 2019.

Hypercalcemia. EBSCO DynaMed Plus website. Available at:http://www.dynamed.com/topics/dmp~AN~T116018/Hypercalcemia.Updated December 27, 2016. Accessed March 6, 2019.

Serum calcium measurement. EBSCO DynaMed Plus website. Available at:http://www.dynamed.com/topics/dmp~AN~T907179/Serum-calcium-measurement.Updated October 8, 2018. Accessed March 6, 2019.

Last reviewed March 2019 by EBSCO Medical Review BoardDianne Scheinberg Rishikof MS, RD, LDN  Last Updated: 3/6/2019